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Thread: Phosphate Removal Additives

  1. #1
    Daihonmei MikeM's Avatar
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    Phosphate Removal Additives

    There are now a number of phosphate removal additives on the market. Typically, they do not reveal their ingredients. This is most likely because the ingredients are available inexpensively if purchased as generic chemicals. My continuing interest in string algae has led me to look into these, but I have found it difficult to get the sort of information that would make me comfortable in any conclusion about use in a koi pond to limit algal growth. So, if anyone has experience using a phosphate remover in a koi pond, please share your experience and be sure to say what product (or chemical) you used.

    There are three main groups of chemicals used to remove phosphate from water in various wastewater and industrial applications. An old common one is aluminium oxide, which can have very unwanted pH impacts.

    The most safely used chemical in aquaria is ferric hydroxide, which will bind not only phosphate but also various organics and metals. It also can contribute to carbonates precipitating and a lowering of pH. In aquaria these impacts on water are generally mild. In a koi pond there could be a greater impact on alkalinity than desired. However, ferric hydroxide involves considerable expense when looking at the amount of phosphate in a koi pond.

    A third group are salts of Lanthanum, a so-called rare earth metal that is not particularly rare at all. The one commonly used in the swimming pool industry is lanthanum chloride, which is comparatively cheap and extremely effective. It has been used by the reef aquarist elite for almost a decade, but users are urgently told that they must avoid lanthanum precipitates (which cloud the water) from getting into the aquarium. The clouding of the water occurs as the lanthanum binds with phosphate, creating a very fine particulate. It eventually settles out. Reports of mass die-offs of corals and other filter feeders are frequent when LC is directly added to a tank. Those lanthanum precipitates are killers of filter feeders. Use in separate vessels has been adopted by some. Others use it in a system where the precipitates are captured by 10-micron and 5-micron filter cloth prior to water returning to the aquarium. This is a wholly impractical level of filtration in a koi pond. Adverse effects on fish, particularly Tangs, have been reported, with it being said that the precipitates irritate and may clog the gills of fish. It is not clear to me, however, that these suppositions are anything more than guesses and reports of actual fish deaths seem too few for me to have any conclusions. Reef aquarists are typically much more interested in their corals and invertebrates than any fish in a reef tank. But, there is certainly cause not to go experimenting with any koi one would not want to lose. There is also lanthanum sulphate, used to some extent, but not enough for any distinguishing traits compared to LC that I can find.

    Of potential interest is lanthanum carboxylate, revealed in a German patent a few years ago. It supposedly does not result in cloudy water. I have not yet learned whether this is because the bound phosphate precipitates are larger/heavier or some other reason. I have not seen any reports of it being used with fish.

    So, altogether, there could be 'who knows what' in those phosphate remover bottles sold under dozens of brands. If there is one that works and is truly safe for koi, with no dramatic effects on water parameters (other than lowering phosphate), it could be a useful tool when string algae strikes.

    Any information to contribute?
    Last edited by MikeM; 03-26- at 05:28 PM. Reason: typo

  2. #2
    Oyagoi yerrag's Avatar
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    Mike, how low should phosphate levels be to effectively control string algae? I used to have phosphate level at the high end of the API test chart, with phosphate at 5 ppm or higher. Now, it has gone down to 2 ppm, yet string algae are still around. In both instances though, they haven't run afoul of me. I'm pretty sure the less the phosphate levels, the better it would be.

    At 4 months into my anoxic system, it may still be too soon to know how much further it can lower my phosphate levels. It would be nice to lower it more with some proven additives.

  3. #3
    Daihonmei MikeM's Avatar
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    Yerrag, I do not have an answer for you. There is no record of experiences with phosphate levels correlated with string algae growth in the koi pond setting. It is my belief that phosphate removal cannot be accomplished in a koi pond to a point where no string algae would grow. In the reef aquaria hobby, where the goal is to have no algae growth, some have a goal of keeping phosphate levels at 0.03ppm or lower. Some are satisfied with, say, 0.1ppm. Many test kits cannot detect at the low levels sought for reef aquaria. Such a low level would be wholly impossible in any practical koi pond. The food we feed adds phosphate in huge quantities. Indeed, phosphorous is needed as part of a well-balanced diet. In many locales around the world, tap water has higher phosphate levels than the reefkeeper desires.

    My thinking is not that string algae can be eliminated through phosphate removal, but that it might be limited. I can imagine use of a phosphate remover at the beginning of an outbreak of excessive growth to curtail or slow growth to a level that does not overwhelm the filtration system.

    The various bottled concoctions currently on the market are something of a mystery to me. They may purport to be 'fish safe', but so do numerous algaecides associated with massive die-offs of koi. If something is 'fish safe when used as directed' and a bunch of folks have bad experiences, I tend to think it is not as safe for fish as I want something to be. But if folks see some benefit and absolutely no harm to their koi, I think it is worth looking into.

    I am still gathering info in regard to Lanthanum chloride experiences (not related to koi thus far), and hope to have something to share in the days/weeks ahead.

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