All about phosphates from Jack's Magic

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
Unfortunately, these are not unbiased sources since Jack's Magic makes phosphate-based metal sequestrants and BioLab does not make phosphate removers but does make algaecides and stabilized chlorine products.

There are several inaccuracies or misleading statements in the articles though some of the conclusions are reasonable. I will enumerate some of these issues here.

  • The R. Neil Lowry article says that "Other forms of phosphate-containing chemicals that contain carbon chains are called organophosphates and normally are not employed as a growth nutrient." This is not true as some organophosphates can be utilized for algae growth. The rest of his article is very good and his conclusions are sound. The BioLabAlgaeLetter says the opposite that "Algae feed on phosphate from sources other than orthophosphates (the only form removed by current products), so they cannot remove even all the sources of this nutrient." This is misleading because the truth is in between. Algae can utilize some organic phosphates but do so more slowly while bacteria can utilize organic phosphates more quickly as described in this paper and this paper. Of course, with chlorine in the pool, there will be virtually no bacterial growth so phosphate removers can at least take the edge off of rapid algae growth even if they do not stop such growth completely. Use of such products isn't necessary if one prevents the growth using chlorine alone at the appropriate FC/CYA ratio.[/*:m:3tyvs9ip]
  • The FAQ-PhosphateFacts article says that nitrates can increase chlorine demand, but it should be noted that this demand is the same as from phosphates, namely increased growth rates in algae and that sufficient chlorine (or algaecide) levels will stop such growth and therefore prevent the resulting chlorine demand. The FAQ also says that "By maintaining a constant level of 1.0 ppm or higher free chlorine in the poor or spa, algae should normally not be a problem." The BioLabPhosphatePaper says something similar in terms of 1-3 ppm FC being all that is needed. These statements are only true if there is little CYA in the water; otherwise the FC/CYA ratio needs to be at least around 5% in SWG pools and 7.5% in manually dosed pools to prevent such growth (under ideal growth conditions with plenty of phosphates and nitrates).[/*:m:3tyvs9ip]
  • The BioLabAlgaeLetter complains about an article that refers to phosphate removers that "remove the algae's food source" because it is just one of the sources (nitrogen and sulfur being the others), but this ignores the fact that all of these are essential nutrients and limiting ANY ONE of them prevents algae growth (though with phosphates, even some simple organic phosphates must be removed as well).[/*:m:3tyvs9ip]
  • The BioLabAlgaeLetter talks about how phosphorous is stored in algae cells. Though this is true, it is irrelevant if one is talking about lowering phosphates to prevent unrestrained algae growth -- for algae to grow (i.e. multiply) they need to produce new organic molecules containing phosphate. It is true that a phosphate remover will not kill existing algae (at least not very quickly), but complete removal of all sources of phosphate would stop algae from growing.[/*:m:3tyvs9ip]
  • The BioLabPhosphatePaper states that "Scientific evaluation demonstrates that phosphates and chlorine do not react to each other or that any depletion of chlorine occurs." The first part of this statement is correct, but the latter part is incorrect if the chlorine level is not sufficient to prevent algae growth. The BioLab tests most likely did not include the FC and CYA levels they recommend of 1-3 ppm FC with up to 200 ppm CYA. In my own pool with 3 ppm FC and 150 ppm CYA years ago, algae was able to grow faster than chlorine could keep up with killing it, and this was in spite of using PolyQuat 60 though only every other week (had I not used algaecide at all, I probably would have had this situation come up when the CYA level was somewhere around 50-80 ppm).[/*:m:3tyvs9ip]

The basic conclusions are sound:

  • Chlorine alone can be used to control algae if the appropriate FC/CYA ratio is maintained. This is true in spite of "ideal" nutrient levels of phosphates and nitrates because there is still a limit to growth rates due to sunlight and temperature.[/*:m:3tyvs9ip]
  • Higher chlorine demand in the presence of high phosphate levels comes from faster algae growth and not from any direct interaction between chlorine and phosphate. Such demand will not occur if proper active chlorine levels are maintained.[/*:m:3tyvs9ip]
  • Phosphate removers only remove orthophosphate so cannot completely stop algae growth if organic phosphates are present, but can slow it down to take the edge off of such growth. Such growth will not occur if proper active chlorine levels are maintained.[/*:m:3tyvs9ip]

Phosphate removers should be seen in the same vein as algaecides such as PolyQuat 60 in that they do not completely eliminate algae growth, but can slow it down such that lower active chlorine levels can be used. It is more like insurance -- you don't need it, but it's an option that costs more and is beneficial if you believe you will not be able to or are unwilling to maintain an appropriate FC/CYA ratio at all times.



Well-known member
Aug 6, 2008
Chem Geek,

Well, as usual learnt a something; thank goodness I maintain a high enough ratio of FC to CYA and no longer use phospate remover and Algaecide 60.

Thank you

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