Why algae killers other than chlorine?

[Flash73]

I've ready many posts, guides, and tips on this page. I believe the "don't add it if you don't need it" philosophy. What I haven't figured out along those lines, since chlorine is cidal (kills) to algae, under what conditions would I need an algaecide other than chlorine? One point, somewhere I read that it can take a free chlorine level of 30 to kill some algae (ie a significant shock level). But having said that, why would I need copper, quat, etc? Thanks.

[Watermom]

Short answer is .......... you don't. It is not necessary to use any algaecide if you maintain proper chemistry in your pool. I don't use any. A few years back, I used 60% Polyquat upon closing my pool. But, I don't even do that anymore. Algaecide is a pretty good preventative, but doesn't do so much for you after you already have an algae bloom. Some people use it when they are going to be away from their pools for awhile to try and head off an algae bloom. But, it is not needed routinely.

As far as copper goes, you do NOT want copper in your pool. Contrary to popular belief, it is copper, not chlorine, that turns blonde hair green.