Comparative Algaecide Efficacy

[chem geek]

The 1980 paper Laboratory Comparison of the Effectiveness of Several Algicides on Isolated Swimming Pool Algae by R.P. Adamson and M.R. Sommerfeld came to the following conclusion:

In summary, results of a laboratory evaluation of the effectiveness of several types of readily available commercial algicides on isolated swimming pool algae demonstrate that at manufacturer's recommended concentrations only chlorine was algicidal to all four species tested. Quaternary ammonium and the silver-containing compound (Algaedyn) were, however, algicidal to the blue-green algae. At higher concentrations (4x recommended concentration), quaternary ammonium became algicidal to the green and yellow-green algae, whereas Algaedyn did not. Algimycin was algistatic to the green alga and exhibited little capacity for controlling the bluegreen and yellow-green algae. The copper-containing compound, Bio-Gard, was ineffective as an algicide at recommended concentrations, since it was not algicidal to any of the test algae and was only algistatic to the yellow-green alga P. pyrenoidosa. Further studies are anticipated to determine whether similar results are obtained for these algicides under actual swimming pool conditions.

It was noted earlier in the paper that "The major component of the active ingredients of Algimycin (poly[oxyethylene-(dimethylimino)-ethylene-(dimethylimino)-ethylene-di-chloride])" which is Polyquat, but it also contained some simazine.

Note how chlorine was the most effective algaecide against all species and the product used was Trichlor. However, the way the experiment was done, the active chlorine concentration would be too high since there was no initial CYA in the water. As with the earlier Adamson/Sommerfeld experiments, the experimental method left something to be desired.

The report Effectiveness of a Chelated Copper Algicide on Algae Grown Under Differing Water Column Phosphorus Regimes showed that 0.4 mg/L of copper was effective while the paper Algicidal effectiveness of Clearigate, Cutrine-Plus, and copper sulfate and margins of safety associated with their use showed that around 0.06 to 0.2 mg/L was effective depending on product (the lowest was copper sulfate which is not chelated so that makes sense). Of course, the main risk with copper is metal staining of plaster surfaces and turning blond hair greenish so one must carefully control the concentration of copper and the pH when using such products.

 

[stev32k]

I wonder if there are any more recent papers on the subject. Surely the manufacturers have read or at least heard of the test results in that paper, and I would hope they have improved their product or revised the usage instructions?

 

[chem geek]

Look at the link in this post for a study done by FMC possibly in 1993, but for algicides used in cooling water treatment (though Polyquat was one of those studied).

There unfortunately isn't a lot on algaecides used in pools. Algae is a nuisance, not a health threat, so isn't something most scientists/researchers look into. I wouldn't necessarily trust industry studies but there aren't many of those either. There's an earlier 1979 paper Comparative Algicide Evalutations Using Laboratory And Field Algae but just shows that if you use higher doses you get more algae inhibition and unfortunately they don't disclose the ingredients of the Algimycin 400 that was used except to say that they were organic compounds and not quaternary ammonium compounds. The EPA requires tests for products to be called algaecides (under registered pesticides), but that doesn't mean they work under all conditions or for all algae types.

The paper Pseudomonas aeruginosa for the Evaluation of Swimming Pool Chlorination and Algicides that I've referred to before in discussing the chlorine/CYA relationship also talks about algicides, but in the context of a bacteria. It notes that pools with higher cyanuric acid levels had higher levels of Pseudomonas aeruginosa which of course is not a big surprise, but it also notes that using quaternary ammonium-based algicides have a similar effect. I should note that they are largely referring to what are known as "linear quats" and not to Polyquat.