I am new at this. How often can H2O2 be used to kill algae?

Re: Caution

anonapersona said:

This can kill fish, so err on the side of caution. I would not exceed 5ml/10 gallon. Actually I'd stop way short of that

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I've safely gone up to 20ml/10 gallons without any problems to fish or snails. Hornwart, riccia and other non rooted plants do have problems however, if you can, remove them prior to treating. For BBA, spot treatment works best, for other forms of algae whole tank treatment is often easier. Obviously as others said, it's not a solution to an algae problem, just an aid in cleaning it up. Work on solving the source of the algae as it will only come back if you don't.

Here's more info for you:
http://www.gpodio.com/h2o2.asp

Hope that helps
Giancarlo Podio