下面引用由baboo在 2004/11/03 05:48pm 發表的內容：
兩隻小魚的Phosban 及Rowa-phos 沒問題. Seachem, Kent 的不要用.(含鋁成份, 有毒啊.中毒現象為漸漸不開然後 RTN!!)

按一下展開……

兩隻小魚的Phosban實在是太貴了....小小小一罐要價900.....
請教一下Baboo兄
我看了kent罐子上面的說明
他說
This product will not release soluble aluminum ,compounds into your aquarium, causing negative reaction from your invert, as competing products may.
意思是(翻譯給大家看)
這產品不會釋放可溶性的鋁或混合物到您的缸子,造成您的軟體不好的反應,(後面那句亂翻)選其他產品可能會.
請問您是從國外網站上得知這kent會釋放鋁的訊息嗎??
還是您有量測水中有鋁呢??
希望您有機會回覆一下此文

我很確定白的都會釋放鋁, 主要是高PH (>7) .
RC 及Advanceaquarist 都有相關文章或討論.
有提到Seachem 的最嚴重.

謝謝Baboo兄的回覆
那我還是拿去換鍶鉬添加劑吧
另有一不情之請
方便把rc上的討論kent及seachem的phosphate sponge相關網址po上來嗎?
小弟感激不盡

那可以把白色的吸附劑放在PH<7的地方像是..........鈣反裡或是置於鈣反出水口嗎........

http://www.advancedaquarist.com/issues/sept2002/chem.htm
http://www.advancedaquarist.com/issues/july2003/chem.htm

下面引用由shiang在 2005/01/08 00:28am 發表的內容：
那可以把白色的吸附劑放在PH<7的地方像是..........鈣反裡或是置於鈣反出水口嗎........

按一下展開……

沒用吧，鈣反流量太小了
相對的，通過吸附性濾材的水流少，處理速度及量也就"小很多"
這邊PH<7應該是指大部分淡水環境

謝謝Baboo兄^^

不過小弟點了之後進不去(IE當掉)
請問有人可以把原文傳訊或在此po上來嗎??
謝謝

Phosphorus: Algae’s Best Friend
Phosphorus is one of the basic building blocks of living matter. It is present in every living creature, and in the water of every reef tank. Unfortunately, it is present in excess in many reef tanks, and that excess has the potential to cause two big problems for reef keepers. The first is that is can drive excessive growth of undesirable algae. The second is that it can directly inhibit calcification by corals and coralline algae. Since most reef keepers don’t want either of these things to happen, they strive to keep phosphorus levels under control.
Fortunately, there are some effective ways of keeping phosphorus concentrations to acceptable levels. Unfortunately, the means for testing for total phosphorus are not trivial. One can readily test for one of the common forms of phosphorus in reef tanks, inorganic orthophosphate, but testing for organic phosphorus compounds is considerably more tedious. Moreover, if there is an algae “problem”, then the algae may be consuming the phosphate as fast as it enters the water, masking the issue. Consequently, reef keepers may not recognize that they have a phosphorus problem, only that they have an algae problem.
This article describes some of the issues around phosphorus in reef tanks, including the forms that it takes, its origins, ways to test for it, and most importantly, ways to export it.

Phosphate in Seawater
The “simplest” form of phosphorus in reef tanks is inorganic orthophosphate (sometimes called Pi by biologists). It is also present in natural seawater, although other forms do exist there as well. Its concentration in seawater varies greatly from place to place, and also with depth and with the time of day. Surface waters are greatly depleted in phosphate, relative to deeper waters, due to biological activities that serve to sequester phosphate in organisms. Typical phosphate ocean surface concentrations are very low by reef keeping standards, sometimes as low as 0.005 ppm.


The structure of orthophosphate, with a central phosphorus atom (purple) and four oxygen atoms (red) arranged in a tetrahedron.
At concentrations below about 0.03 ppm, the growth rate of many species of phytoplankton is dependent on the phosphate concentration (assuming that something else is not limiting growth, such as nitrogen or iron). Above this level, the growth rate is independent of phosphate concentration for many organisms. So if you want to deter algae growth by controlling phosphate, you need to keep phosphate levels quite low.
In order to best understand how to maintain appropriate phosphate levels, we must first understand our quarry. Orthophosphate consists of a central phosphorus atom surrounded by four oxygen atoms in a tetrahedron (Figure 1). Orthophosphate exists in various forms in seawater, depending on the pH. At pH 8.1, seawater contains 0.5% H2PO4-, 79 % HPO4--, and 20% PO4---. At higher pH the equilibrium shifts toward more PO4--- and less HPO4--.
The shift in distribution with pH may seem esoteric, but it actually has important implications for such things as the binding of phosphate to rock and sand. It may also surprise some people that so much of the phosphate is present as PO4--- while in fresh water only 0.1% is present in that form at the same pH. There are a number of reasons for this difference between salt water and fresh water that involve the effects of other ions in the seawater on the phosphate (such as calcium and magnesium ion-pairs), and these have been described previously.

Other Forms of Inorganic Phosphate
Phosphorus can also take other inorganic forms, such as the polyphosphates which are rings and chains of phosphate ions strung together by P-O-P bonds. While these are not significant in natural seawater, they can be present in things that get added to our tanks. There are many of these compounds, but most will likely break down into orthophosphate when added to a reef tank.
Polyphosphates are used industrially to bind metals, such as in some laundry detergents. In that application, they form soluble complexes with calcium and magnesium, softening the water and permitting better cleaning action. The amount of phosphate getting into natural waterways from laundry detergents, however, is high enough that algae blooms sometimes result, and the practice is now illegal in many places.

Organic Phosphates
Unfortunately for reef keepers, the world of organic phosphorus compounds is far more complex than inorganic phosphates. Many common biochemicals contain phosphate esters. Every living cell contains some. Molecules such as DNA, ATP, phospholipids (lecithin), and many proteins contain phosphate groups. In these molecules, the basic phosphate structure is covalently attached to the remainder of the organic molecule through one or more phosphate ester bonds to a carbon atom.
These bonds are stable for some period of time in water, but will eventually break down to release inorganic orthophosphate from the organic part of the molecule, a process that can be sped up through the action of enzymes in a reef tank. Many of these organic phosphate compounds will be readily removed from a tank by skimming. Export of organic phosphates is the major way that skimming can result in reduced inorganic orthophosphate levels in a tank. Orthophosphate ions themselves are not significantly removed via skimmate (since they do not adsorb onto an air/water interface), but organic phosphates can be removed before they are converted into inorganic orthophosphate.
An important point about organic phosphates is that they will mostly not be impacted by phosphate-binding materials sold to the aquarium hobby. Consequently, while these products may do a fine job of reducing inorganic orthophosphate, they may not help an algae problem that is caused primarily by organic phosphates.
A final point is that organic phosphates will not be detected by most test kits. Those that do detect organic phosphates (e.g., Hach PO-24) break the phosphate off of the organic compound and thereby convert it into inorganic orthophosphate prior to testing. However, these kits are tedious and expensive, and not for every hobbyist.



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Phosphate Sources in Reef Tanks
Organic phosphorus compounds, as well as orthophosphate, are so prevalent that any natural food will contain significant concentrations of phosphorus. Flake fish food is typically about 1% phosphorus (3% phosphate equivalent) by weight. Consequently, if 5 grams of flake food is added to a 100 gallon tank, there is the potential for the inorganic orthophosphate level to be raised by 0.4 ppm in that SINGLE FEEDING. That fact can be a significant issue for reef keepers: what to do with all of that phosphorus?
If the food is completely converted into tissue mass then there will be no excess phosphate. But much of the food that any organism consumes goes to provide energy, leaving a residue of CO2, phosphate, and a variety of nitrogen-containing compounds. A fish, whether it is an adult or a growing juvenile will consequently excrete much of the phosphorus that it takes in with food as phosphate in its waste. Of course, overfeeding will result in more delivery of phosphate than will lower feeding levels.
Additionally, many types of seafood available at the grocery store have various inorganic phosphate salts intentionally added to them as preservatives. These foods include canned and frozen seafood, as evidenced by the label, and even some fresh seafood. In these cases, rinsing the food before using it may help reduce the phosphate load added to the tank.
Finally, tap water can be a significant source of phosphate. The tap water supplied by the Massachusetts Water Resources Authority to me is acceptably low in phosphate, or at least it was the last time that I measured it a few years ago (I use RO/DI due to excessive silica in it). In other water supplies, however, phosphate levels can be too high. I’d recommend anyone with an algae problem who uses tap water to test to see if phosphate in the water is a possible issue.
On the other side of the issue are those tanks without fish. Since phosphorus is required for growing tissue, it is mandatory that there be some phosphorus source for corals growing in a reef tank. Finding a source is trivial if there are fish in the tank that require feeding, but in tanks without fish, reef keepers must somehow add phosphorus. The answer to this question is rather easy: either add fish food even though there are no fish, or add a source of phosphorus such as a plant fertilizer (and don’t forget about a source of nitrogen as well).

How to Export Phosphate
So now that we know where phosphate comes from, and how much, we can proceed to ask where it goes and how to maximize those export processes. Certainly, some phosphorus goes into the bodies of growing organisms, including bacteria, algae, corals, and fish. Some of these organisms stay permanently in the tank, and others may be removed by harvesting of algae, skimming of small organisms, and even pruning of corals.
A less frequently discussed mechanism for phosphate reduction may simply be the precipitation of calcium phosphate, Ca3(PO4)2. The water in many reef tanks will be supersaturated with respect to this material, as the equilibrium saturation concentration in normal seawater is only 0.002 ppm phosphate. As with CaCO3, the precipitation of Ca3(PO4)2in seawater may be limited by kinetic factors more than equilibrium factors, so it is impossible to say how much might precipitate under reef tank conditions (without, of course, somehow determining it experimentally). This precipitation may be especially likely where calcium and high pH additives (like limewater) enter the tank water. The locally high pH converts much of the HPO4-- to PO4---. Combined with the locally high calcium, the locally high PO4--- may push the supersaturation of Ca3(PO4)2 to unstable levels, causing precipitation.
Likewise, phosphate can precipitate onto the surface of calcium carbonate, such as onto live rock and sand. The absorption of phosphate from seawater onto aragonite is pH dependent, with the maximum binding taking place around pH 8.4 and with less binding at lower and higher pH values. If the calcium carbonate crystal is static (not growing), then this process is reversible, and the aragonite can act as a reservoir for phosphate. This reservoir can make it difficult to completely remove excess phosphate from a tank that has experienced very high phosphate levels, and may permit algae to continue to thrive despite cutting off all external phosphate sources. In such cases, removal of the substrate may even be required.
The relationship of calcium carbonate to the phosphate cycle has been studied by Frank Millero in the Florida Bay ecosystem (click here for Millero's studies). If aragonite crystals are growing, as they often are in some parts of our systems, then I’d expect some of this phosphate to get buried and locked into the aragonite crystals.
A side effect of the adsorption of phosphate onto aragonite may well be the reported impact of phosphate on the calcification of corals. The presence of phosphate may inhibit the formation of calcium carbonate crystals via surface adsorption, and this effect may very well be the factor that inhibits calcification of corals at high phosphate levels.
Many reef keepers accept the concept that limewater addition reduces phosphate levels. This may be true, but the mechanism remains to be demonstrated. Craig Bingman has done a variety of experiments related to this hypothesis, and published them in Aquarium Frontiers. While many may not care what the mechanism is, knowing it would help to understand the limits to this method, and how it might best be employed.
Habib Sekha (the owner of Salifert) has pointed out that limewater additions may lead to substantial precipitation of calcium carbonate in reef tanks. This idea makes perfect sense. After all, it is certainly not the case that large numbers of reef tanks will exactly balance calcification needs by replacing all evaporated water with saturated limewater. And yet, many find that calcium and alkalinity levels are stable over long periods with just that scenario. The only way that can be true is if such additions typically dump excess calcium and alkalinity into the tank that is subsequently removed by precipitation of calcium carbonate (such as on heaters).
It is this ongoing precipitation of calcium carbonate, then, that may reduce the phosphate levels: phosphate binds to these growing surfaces, and becomes part of the solid precipitate. If true, this mechanism may be attained with other high pH additive systems (like some of the two-part additives such as the original B-ionic) if enough is added. However, it will not be as readily attained with low pH systems, such as calcium carbonate/carbon dioxide reactors because the low pH inhibits the precipitation of excess calcium and alkalinity.

Uptake of Phosphate by Organisms
How organisms obtain phosphate is, in nearly all cases, poorly understood. Even the absorption mechanisms used by humans are still the subject of intense research (one of my research areas involves drugs to modify this absorption, such as Renagel). It’s not surprising then that phosphate absorption mechanisms in coral reef creatures would also be poorly understood.


A handful of Chaetomorpha sp. macroalgae being harvested from the authors refugium.
One frequently hears that limiting phosphate will limit algae growth in reef tanks. That is almost certainly true, but some species of microalgae thrive more readily under phosphate limitation than others (click here for phosphate limitation studies). Some species of microalgae can, in fact, significantly regulate their inorganic phosphate transport capabilities to deal with variable phosphate levels (click here for Upregulation of Phosphate Transport).
Finally, one must also consider organic phosphates. Many organisms can enzymatically break down organic phosphates prior to absorption. Consequently, we are left not having a very good understanding of what organisms in our tanks use what forms and concentrations of phosphorus. Further complicating matters, our tanks are usually greatly skewed from natural seawater in terms of other nutrients (e.g., nitrogen and iron), so one cannot readily extrapolate from phosphate studies in seawater to our tanks.
Nevertheless, growing and harvesting macroalgae (Figure 2) remains one of the best ways to reduce phosphate levels in reef tanks (along with other nutrients). Tanks with large amounts of thriving macroalgae rarely have microalgae problems or excessive phosphate levels that might inhibit calcification of corals. Whether the reduction in phosphate is the cause of the microalgae reduction is not obvious; other nutrients can also become limiting. But in a certain sense it makes no difference. If rapidly growing macroalgae absorb enough phosphorus to keep the orthophosphate concentrations in the water column acceptably low, and at the same time keep microalgae under control, most reef keepers will be satisfied.
For those interested in knowing how much phosphorus is being exported by macroalgae, this free pdf article in the journal Marine Biology has some important information. It gives the phosphorus and nitrogen content for 9 different species of macroalgae, including many that reefkeepers maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08 % by dry weight phosphorus and 5.6% nitrogen. If one were to harvest 10 grams (dry weight) of this macroalgae from a tank, it would be the equivalent of removing 24 mg of phosphate. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67 gallon tank. All of the other species tested gave similar results (plus or minus a factor of 2). Interestingly, using nitrogen data in the same paper, it would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same tank.



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Commercial Products
There are, of course, many commercial products for reducing phosphate concentrations. Typically, these only reduce inorganic orthophosphate, but they can do that effectively, if not inexpensively. Two of the main types are those based on aluminum oxide (such as Seachem’s Phosguard) and those based on iron oxides and hydroxides (such as Rowaphos). Many people have successfully used these products (including myself), but others claim problems from the aluminum products that they blame on aluminum toxicity. I’ve seen no basis for these claims in my own tank, but I did not use them long term.
My advice on these products is that they can be used successfully, but that there may be better, and certainly less expensive and more interesting ways to reduce phosphate levels (such as setting up a refugium with macroalgae in it).

Summary of Phosphate Reduction Methods
Here is a list of ways that people can reduce phosphate levels. They are listed in order of preference that I have for addressing these issues in my own system:
1. The big winner is macroalgae growth. Not only does it do a good job of reducing phosphate levels, but it reduces other nutrients as well (e.g., nitrogen compounds). It is also inexpensive and may benefit the tank in other ways, such as a haven for the growth of small life forms that help feed and diversify the tank. It is also fun to watch. I’d also include in this category the growth of any organism that you routinely harvest, whether corals or something else.
2. Skimming is another big winner, in my opinion. Not only does it reduce organic forms of phosphate, but it reduces other nutrients and increases gas exchange. Gas exchange is an issue that many people don’t recognize, but that can contribute to pH problems.
3. The use of limewater, and possibly other high pH alkalinity supplements, is also a good choice. It can be very inexpensive, and it solves two other big issues for reef keepers: maintaining calcium and alkalinity.
4. Commercial phosphate binding agents clearly are effective.
5. Simply keeping the pH high in a reef tank (8.4) may help keep phosphate that binds to rock and sand from reentering the water column. Allowing the pH to drop into the 7’s, especially if it drops low enough to dissolve some of the aragonite, may serve to deliver phosphate to the water column. In such systems (typically those with carbon dioxide reactors), raising the pH may help control soluble phosphate.

Summary
Issues involving phosphorus can be among the most difficult to diagnose in a reef tank, especially if the live rock and sand have been exposed to very high phosphate levels and may be acting as a phosphate reservoir. Fortunately, there are steps that can be taken even in the absence of any algae problem that will benefit reef tanks in a variety of ways, not the least of which is reduction of phosphate levels. All reef keepers, and especially those designing new systems, should have a clear idea in mind about how they expect phosphorus to be exported from their system. If allowed to find its own way out, it will more than likely end up in microalgae that the reef keeper is constantly battling.

To access our Chemistry forum to discuss this article, click here
Copyright 2002 Advanced Aquarist's Online Magazine

Aluminum in the Reef Aquarium

Aluminum is an ion that doesn’t get much discussion in reefkeeping circles. It has little in the way of positive biological functions. I am not aware of any marine organisms with a demonstrated requirement for aluminum. It can, however, be toxic to marine organisms at elevated levels. Occasionally, folks discuss whether metal devices made from aluminum alloys will corrode in seawater. Most often, aluminum comes up during discussions of aluminum-based phosphate binding agents. These aluminum oxide materials have been reported to cause negative reactions in certain corals, and one hypothesis that has been suggested is that aluminum is released that irritates the corals.
In this article I will give some details of aluminum in natural seawater, and will discuss the sparse literature on the toxicity of aluminum ions to marine organisms. I will also show that aluminum is indeed released from one of these types of materials (Phosguard, sold by Seachem). Finally, I will show whether added soluble aluminum irritates any of several corals in a test aquarium.

Aluminum in the Ocean
Individual soluble aluminum ions in the ocean largely take the form Al(OH)4-, but some are also present as Al(OH)3.1,2 Aluminum is also strongly attracted to organics and some inorganics (like silica), making the exact speciation of aluminum very complicated. There is also a fair amount of aluminum present in particulate and colloidal forms (typically in combination with silica), ranging in concentration from about the same as the soluble fraction, to much greater.3-6
Interestingly, aluminum is present at much higher total concentration in the Gulf of Mexico (~0.002 ppm for particulate forms only),4 the Atlantic Ocean (0.00014 – 0.0016 ppm))8-12 and the Mediterranean Sea (0.00008 – 0.02 ppm)3 than in the Pacific Ocean (0.0000016 – 0.00016 ppm)7,8 or near Antarctica (0.00008 ppm).9 This difference provides a significant clue to the origin of most aluminum in surface seawater: airborne dust landing in the water.7,10-12 Dust from Africa is the proposed reason why the Atlantic is so much higher in concentration,9,12 while some in shore areas are also elevated due to the input from rivers.
The maximum solubility of aluminum at pH 8.2 in freshwater is about 2.7 ppm.13 That is, at concentrations higher than that, the aluminum will precipitate as amorphous aluminum hydroxide. I expect the solubility to be similar or higher in seawater, where complexation to organics may increase the solubility. Consequently, the solubility in both the oceans and in aquaria (as will be seen below) is apparently not typically limited by the solubility of aluminum hydroxide itself.

Biological Effects of Aluminum: Toxicity
There are many known biological effects of aluminum, nearly all of which are negative.14 Aluminum toxicity has been extensively studied in fish, especially freshwater fish, but less so in other organisms, including marine fish.15 In freshwater systems, the toxicity of aluminum is a function of pH, with aluminum typically more toxic at lower pH. The reasons for this include the solubility, the speciation, and the nature of the interaction of aluminum with the surfaces of organisms as the pH changes.14 At pH 7, aluminum can bind to the gills of fish, inducing asphyxiation.15
Toxicity studies in marine systems has been much more limited. The table below describes some of the data:

Table 1. Toxicity of aluminum to marine organisms

Species Tested
Endpoint
Concentration
Reference

Cancer anthonyi (a crab)
7 day lethal concentration
10 ppm
16 and Web site

Crustaceans (4 species)

3-4 day lethal concentration
0.24-10 ppm
Web site

Mollusc

3 day lethal concentration
2.4 ppm
Web site

Ctenodrilus serratus (polychaetous annelid)
4 day lethal concentration
0.1 ppm
17 and Web site

Capitella capitata
(polychaetous annelid)
4 day lethal concentration
0.4 ppm
17 and Web site

Neanthes arenaceodentata
(polychaetous annelid)
4 day lethal concentration
>0.4 ppm
17 and Web site



Biological Effects of Aluminum: Uptake
In addition to suffering from overt toxicity, many organisms take up aluminum, and some have developed systems to deal with aluminum that they apparently don’t want. In freshwater snails, for example, it has been suggested that silica is used to detoxify aluminum:18,19

“These findings, and arguments on the stability, lability, and kinetics of aluminum-silicate interactions, suggest that a silicon-specific mechanism exists for the in vivo detoxification of aluminum,”19

In marine systems, diatoms similarly take up aluminum and it is reported that it can impact their growth.20,21 The absorption of aluminum was recently studied in detail in the marine phytoplankton Dunaliella tertiolecta (a unicellular green algae).22 The bioaccumulation was found to be strongly related to the aluminum concentration in the seawater (Figure 1). Consequently, one might expect that whatever problems aluminum causes, that it could be more severe as aluminum levels increase up to 1 ppm, at least for this particular organism. This result is important as that is the range of aluminum concentration that can result from exposure to Phosguard (later in this article).


Figure 1. Bioaccumulation of aluminum by the green alga Dunaliella tertiolecta.22



Aluminum in Reef Aquaria
In a recent survey of 23 reef aquaria, Shimek claimed that aluminum levels ranged from 0.070 to 0.32 ppm, with a mean of 0.173 ppm .23 That same study claimed that Instant Ocean Contained 0.110 ppm aluminum. Other than values reported later in this article, I am not aware of any other published values for aluminum in reef aquaria.



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These values were all generated by ICP (Inductively Coupled Plasma) where the sample is injected into a plasma and the light emissions of the various ions are quantified at one or more specific wavelengths unique to each element. I am skeptical that all of the values in the survey above represent real measurements of aluminum rather than noise in the ICP since they are all right around the limit of quantitation for aluminum in seawater. While this issue may seem esoteric, it is important to know how much aluminum is typically present in aquaria in order to understand whether the aluminum leached from products such as Phosguard represent a significant addition, or a trivial amount.
The following section discusses details of ICP testing for aluminum in seawater that may not interest most aquarists. It is intended to justify the skepticism about the measurements reported above. If one accepts the premise that those values may be unreliable, or if one just doesn’t care about such things, then skip on down to the next section, entitled “Inputs of Aluminum in Reef Aquaria: Salt Mixes.”

As part of the experiments to test for the release of aluminum from Phosguard, I tested a sample of water from my aquarium as well as freshly made Instant Ocean (both at a salinity of 35 ppt). I used a new Varian ICP-OES in an attempt to detect aluminum in these samples (none were acidified or filtered unless otherwise noted). However, I was unable to detect anything but noise in these samples. That is, in looking at the emission spectra themselves, I simply saw a noisy background by eye, without any significant peak at the known emission wavelengths for aluminum (I used 237.312, 308.215, 394.401, and 396.152 nm). Spiked samples (standards made by adding soluble aluminum to the samples of aquarium water and Instant Ocean salt mix), and those where aquarium water or Instant Ocean water were exposed to Phosguard (below) did have clearly defined peaks at these wavelengths.

Figure 2:The ICP emission spectrum between 237.2 and 237.4 nm of a sample from my aquarium (blue) and the same sample after being spiked with 0.5 ppm aluminum (red).

Figure 2 shows some typical ICP data for these samples. The blue line represents the emission spectrum displayed by my aquarium water sample. It is actually the average of three testing replicates taken from a single water sample. The red line represents the same sample with 0.5 ppm aluminum spiked into it. Clearly, the spiked aluminum gives a clearly defined signal exactly where it is supposed to be, while the aquarium water sample shows no such peak. This same conclusion applied at each wavelength examined, and for the Instant Ocean samples as well. From these data, I conclude that the concentrations of aluminum in my aquarium sample and in Instant Ocean are less than 0.05 ppm aluminum.
Nevertheless, the device software for the ICP is what most laboratories will use to quantify ions in high volume samples submitted for analysis. When I used the Varian software to determine the concentration in these samples, it integrated the noise in these samples to the equivalent of 0.05 – 0.12 ppm aluminum for both samples (and for each of several wavelengths used). Likewise, 18 mega-ohm deionized water (very pure) came out at 0.04 to 0.11 ppm aluminum. Consequently, the background noise, and the reality or not of the emissions being quantified must be carefully considered when reporting values near the noise limit for the device.
Was this an important issue for the samples analyzed for aluminum by Shimek? Is that why the samples all looked fairly similar in terms of aluminum concentration? Do any of those reported values represent real determinations, or simply background noise? I don’t know, but I am skeptical. Since I am not aware of any other measurements of aluminum in reef aquaria, I believe that we are left without knowing what the concentrations are, except that in the case of my aquarium at least, the concentration is ≤ 0.05 ppm.

Inputs of Aluminum in Reef Aquaria: Salt Mixes
In their study of artificial saltwater mixes, Atkinson and Bingman claimed that 8 different artificial salt mixes contained between 6 and 8 ppm aluminum (which they reported as 230-290 μmole/kg).24 Because the numbers are all so similar and so very much higher than my test (≤0.05 ppm for Instant Ocean) or those reported by Shimek (0.1 ppm for Instant Ocean), or the S-15 Report (0.006 ppm aluminum in Instant Ocean; similarly low for the other mixes tested), I suspect that the Atkinson and Bingman aluminum values may represent an artifact of some sort, either in testing or in data tabulation. Consequently, the starting artificial salt max may not be an especially important source of aluminum in aquaria (especially as compared to other inputs described below).


Figure 3. The leather coral in the test aquarium prior to addition of soluble aluminum

Figure 4. The leather coral in the test aquarium after addition of aluminum. After the addition, it cycled between the look in this photograph, and that shown in Figure 3.


Inputs of Aluminum in Reef Aquaria: Foods
Foods are, of course, another potential source of aluminum. In a study of the amounts of different elements in certain foods,25 Shimek presented the results shown in Table 2. The values have also been normalized to show the amount of aluminum in the foods in relation to the number of calories provided. Clearly, if aluminum is of primary concern, brine shrimp (highlighted in red) should probably not be on the menu.
If you fed 5 grams of it to a 100 gallon tank every day, that would amount to 5 g x 120 mg/kg = 0.6 mg/day or 219 mg/year. Added to that 100 gallons (379 L), that gives an addition of 219 mg/378 L/y = 0.6 ppm per year. The other listed foods would, of course, contribute much less. Unfortunately, these sorts of raw measures of aluminum say nothing about what form it is in. For example, it might be present as soluble aluminum, or as insoluble (particulate) forms.


Table 2. Aluminum content of various aquarium foods.

Food
Calories/gram
Total Aluminum (ppm)
Aluminum (mg/kcalorie)

Formula One
0.8
15
19

Formula Two
0.8
15
19

Prime Reef
0.8
11
14

Lancefish
0.9
9.8
11

Brine Shrimp
0.3
120
400

Plankton
0.7
8.1
12

Gold Flakes
4.2
80
19

Tahitian Blend
2.4
14
6

Saltwater Staple
3.6
95
26

Nori
3.6
83
23

Golden Pearls
3.9
49
13



Inputs of Aluminum in Reef Aquaria: Calcium and Alkalinity Supplements
Another significant source of aluminum are the calcium and alkalinity supplements that aquarists use. In a recent paper on metals in aquaria,26 I quantified some of these inputs, and the results for aluminum are summarized below.
Limewater (kalkwasser) is made by dissolving calcium oxide or calcium hydroxide in water. The calcium oxide that I use from the Mississippi Lime Company is food grade, but still has certain impurities. The typical analysis of this material shows it to contain 0.10 % aluminum. It is not obvious what form this takes but since aluminum is quite soluble at pH 12.4 (total solubility = 80 ppm at pH 12.4,27 if saturated limewater were made from CaO with 0.1% aluminum, it would contain 1 ppm aluminum) it is a reasonable hypothesis that it dissolves into the limewater and is delivered to the aquarium. If one were adding 2% of the aquarium volume in saturated limewater (0.0204 moles/L CaO) every day for a year, one would have added the equivalent of 8.3 ppm aluminum.
The amounts of metals that are added to an aquarium when using a CaCO3/CO2 reactor can also be determined. The impurities present in such media varies with the source or brand of the media, as has been shown in different articles by Craig Bingman 28 and Greg Hiller 29. If we make the assumption that we want the same total amount of calcium and alkalinity as in the limewater case described above, then we can calculate the following amounts of metals added over a year:

Table 3. Cumulative amount of aluminum added to a reef aquarium over the course of a year using a CaCO3/CO2 reactor

Substrate
Amount added in 1 year (ppm)

Conklin Limestone
<0.001

Nature's Ocean
1.2

Koralith
1.0

Super Calc Gold
1.1


As can be seen, the amount added over the course of a year can be quite substantial, but is less than is delivered via limewater (at least in these calculations). To be honest, I’m not sure why there is less aluminum delivered by CaCO3/CO2 reactors than limewater. Calcium oxide is made by heating calcium carbonate until the carbon dioxide is driven off. Such a conversion shouldn’t impact aluminum concentrations. Perhaps the difference simply reflects artifacts in one or both of the testing methods, contaminants in production, or in the nature of the original calcium carbonate chosen for each process.
Other methods of calcium and alkalinity addition presumably also deliver some amount of aluminum, though I’ve not seen any analysis of any of them to comment further.

Inputs of Aluminum in Reef Aquaria: Phosguard
Many aquarists claim to see undesirable effects on corals when using Phosguard, made by Seachem. Many aquarists have attributed that effect to released aluminum, since it is largely composed of aluminum oxide (possibly with silicon present too). In the first phase of testing that hypothesis, I examined whether Phosguard does indeed release any aluminum into solution.
Table 4 summarizes the results for a serious of samples in which commercial Phosguard (75 mL) was placed into contact with aquarium water or freshly made Instant Ocean artificial seawater (500 mL). The samples we allowed to sit in closed plastic containers. Once every 3 days or so the containers where gently shaken for a few seconds. Aliquots were removed, in some cases filtered through a 0.45 μm filter to remove “particulates”, and the aluminum was determined by ICP (without acidification). The concentrations were determined by comparison to standard made by spiking 0.5 ppm aluminum into aquarium water or Instant Ocean artificial seawater (which had been shown earlier in this article to have no detectable aluminum). All of the samples had a clearly definable emission peak in the appropriate place, although the lowest sample (0.06 ppm) is close to the limit of detection.

Table 4. Aluminum Concentration in water samples exposed to Phosguard

Water Sample
Exposure Time
Filtration
Aluminum Concentration (ppm)

Aquarium Water
none
none
≤ 0.05

Aquarium Water
1 week
none
0.37

Aquarium Water
1 week
0.45 μm
0.06

Aquarium Water
5 weeks
none
0.71

Aquarium Water
5 weeks
0.45 μm
0.12

Instant Ocean
none
none
≤ 0.05

Instant Ocean
1 week
none
1.11

Instant Ocean
1 week
0.45 μm
0.13


From the results in Table 4 it is evident that Phosguard does release aluminum to the water, and that the majority of this is present in particulate form (that is, that it is removed on a 0.45 μm filter (although that does not demonstrate that it was originally released as particulates).
In order to determine if these results are caused primarily by fine particles that come with the much larger Phosguard particles (typically about 2 mm spheres), a batch was rinsed very thoroughly with RO/DI water (8 times, with each rinse lasting about 1 minute and each rinse volume comprising about 20 times the solid particle volume). These rinsed Phosguard particles were then exposed to aquarium water as above. The results are shown in Table 5.

Table 5. Aluminum Concentration in water samples exposed to rinsed Phosguard

Water Sample
Exposure Time
Filtration
Aluminum Concentration (ppm)

Aquarium Water
none
none
≤ 0.05

Aquarium Water
2 weeks
none
0.25

Aquarium Water
2 weeks
0.45 μm
0.16


Not surprisingly, the concentration is reduced in the unfiltered sample, indicating that the rinsing may well have removed some fine particles that were contributing to the results in the unfiltered samples. However, the aluminum concentration in the filtered sample is not reduced, indicating that the “dissolved” fraction of the aluminum is not altered by rinsing the Phosguard first.

Significance of Aluminum Release from Phosguard
Is the amount of aluminum released from Phosguard significant? Moreover, is it adequate to explain the results on corals that have been reported by aquarists? This question is extremely difficult to answer without some biological experiments. The tests run above show reasonably high concentrations of aluminum. Possibly high enough to cause problems for the organisms shown in Table 1 . But these tests were carried out on a large amount of Phosguard in a small amount of water. Tests with larger volumes of water might well result in lower aluminum concentrations. Additionally, the exact nature of the aluminum in these tests may well be different than in the toxicity tests reported above. That is, the nature may be particulate vs. colloidal vs. soluble vs. complexed by organics, etc.

Biological Testing of Aluminum Exposure
In order to more definitively show whether aluminum released by Phosguard might be the cause of reaction in corals, it seems prudent to test aluminum on corals. Toward this end, I set up a 30-gallon aquarium with several corals. These included a leather coral (Sarcophyton sp.), green star polyps, and brown mushroom corals. In addition, the tank contained sand, live rock, and some macroalgae (Chaetomorpha sp. and Caulerpa racemosa).
Pictures were taken of the several corals, and then aluminum was added. Figure 3 shows the leather coral before any addition. The first aluminum addition boosted the aluminum concentration by 0.005 ppm by adding 0.15 mL of an aluminum chloride solution to the water. A pH electrode was in the water at the time and recorded no pH change (pH = 8.32). There was no apparent change in any corals in 2 hours.


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The second aluminum addition boosted the aluminum concentration by 0.045 ppm by adding 1.35 mL of an aluminum chloride solution to the water (total additions = 0.05 ppm aluminum). A pH electrode was in the water at the time and recorded a pH drop of from 8.35 to 8.33-8.34 pH. There was no apparent change in any corals in 24 hours.
The third and last aluminum addition boosted the aluminum concentration by 0.45 ppm by adding 1.35 mL of an aluminum chloride solution to the water (total additions = 0.5 ppm aluminum). A pH electrode was in the water at the time and recorded a pH drop of from 8.35 to 8.25 pH. There was no apparent change in any corals in 1 hour. By the 5-hour mark, the leather coral had closed (pH = 8.30), and then it began cycling between open and closed every hour or two, continuing into the next day. Figure 4 shows the closed form.

Thirty six hours after the last aluminum addition, the leather was still cycling between open and closed. This behavior had not been exhibited by this coral prior to aluminum additions. While I cannot be certain it was a result of the treatment, it seems likely.

After 48 hours, the leather no longer opened at all. It then stayed closed for the next 3 days until the termination of the experiment. I’ve since moved it to my main tank in the hope that it will recover.
5 hours after the last aluminum addition, the mushroom corals appeared less expanded than before the aluminum additions, but not nearly as dramatically as the leather. They stayed that way until the termination of the experiment.
The green star polyps seemed unchanged for the first 48 hours. After that, they expanded significantly less than they had previously. The polyps were about half of the size that they were before dosing aluminum. They were still that way at the termination of the experiment.

Conclusions
Aluminum is an ion that does not get much attention, and has no clear biological use in aquaria. It can, however, have an impact on aquarium organisms if elevated sufficiently over natural levels. Phosguard has been shown to release aluminum to artificial seawater. Further, it appears that the release of aluminum could be the cause of the effects that some folks have seen in aquaria when using aluminum-based phosphate and silicate absorbing materials. However, only a larger study could definitively demonstrate that to be the case.
Such biological effects have not been widely reported for the iron-based phosphate removers (e.g., Rowaphos and Salifert’s Phosphate Killer). Consequently, if you are interested in using phosphate-absorbing media, those latter types might be a better choice.
Happy Reefing!


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23. It's (in) the Water by Ronald L. Shimek. Reefkeeping.com. Volume 1. Number 1. February 2002
http://reefkeeping.com/issues/2002-02/rs/feature/index.htm
24. The Composition Of Several Synthetic Seawater Mixes by Marlin Atkinson and Craig Bingman Aquarium Frontiers March 1999.
http://www.animalnetwork.com/fish2/aqfm/1999/mar/features/1/default.asp

25. Necessary Nutrition, Foods and Supplements, A Preliminary Investigation by Ronald L. Shimek. Aquarium Fish Magazine. 13: 42-53.

26. Reef Aquaria with Low Soluble Metals. By Randy Holmes-Farley, Reefkeeping, April 2003
http://reefkeeping.com/issues/2003-04/rhf/feature/index.htm

27. Metals In Limewater by Randy Holmes-Farley, Advanced Aquarist, May 2003
http://www.advancedaquarist.com/issues/may2003/chem.htm
28. Calcium Carbonate for CaCO3/CO2 Reactors: More Than Meets the Eye by Craig Bingman Aquarium Frontiers, August 1997.
29. Alternative Calcium Reactor Substrates by Greg Hiller Aquarium Frontiers.




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