Of late, I've involved myself (foolishly or not) in discussions relating to the value of polyquat algaecides. Believing that 'a little knowledge is a dangerous thing', I've sought to educate myself more completely on the mechanism(s) by which polyquat agents might inhibit algal growth, or, as it is claimed, actually kill algae.
I can accept that, as strong chelating agents, they might act in some way on the algae cell wall, possibly by interfering with cell wall synthesis or otherwise stressing the cells through disruption of cell wall components, but I have difficulty with the explanations cited in some articles and promotional literature that describe polyquats stripping algae (and bacteria, in some accounts) of their walls, leading the poor little denuded blighters to suffer death by lysis. If they were that effective, why are we still using chlorine?
I've read that polyquats are highly effective against the more resistant forms of Mustard and Black algae. I can see how polyquats might aid in disrupting the resistant outer crust of these varieties and possibly loosen their hold on pool surfaces, but then what? Do they actually play a role in killing the cells or merely make them more vulnerable to chlorine?
I can accept that polyquats might stop green algae from getting a foot-hold by preventing slime bio-film formation, possibly even forming a barrier that prevents algae from adhering to pool surfaces. That seems quite plausible.
I can also accept that polyquats might aid in the clearing of chlorine-killed algae by cross-bridging and clumping cells such they fall out of suspension. I am also aware the interaction with chlorine is complicated by the fact that chlorine is itself rapidly oxidized by polyquat, and that, in turn, polyquats are progressively degraded by chlorine.
What I cannot find however is any credible scientific literature that accurately describes the mode of action of polyquat agents on algae and lends support to any of these oft quoted suppositions.
Can anyone point me to such literature?