[cS]

Why doesn't dosing peroxide [...] directly to a tank help?

Yes it does. Most folks aren't dosing enough, and thank goodness they don't because it's not at all safe for fauna.

Six months ago, my 20G was infested with a HEAVY HEAVY infestation of numerous species of algae; the worst of which is BBA. I really didn't feel like tearing everything down and bleach so I did the 2nd best thing (the first is of course being patient and do the nutrient control route ): (1) removed all fauna and (2) dumped ~300 ml of a 3% H2O2 solution (Kroger brand). Within 3 days, all the algae either disappeared or turned white. The plants did not seem to be majorly damaged, except for the mosses/liverworts and the H. zosterifolia had black edges. Did several 50% water changes and lowered light intensity for the next few days to avoid triggering a green water bloom. Afterwards, all the plants resumed photosynthesis as if nothing had happened. I also waited 2 weeks after treatment before adding back the fauna just to be on the safe side.

Now folks, don't get the wrong idea and start dumping H2O2 into your tank because you will surely kill all the fauna and possibly trigger a green water bloom. The point of this post is to point out that H2O2 works if dosed in a high enough concentration and that it's a more convenient alternative to tearing down a tank and bleach everything.

THE FINE PRINT
I would like to point out something very important Mr. Ludwig noted earlier: "Focus on growing plants not on preventing algae..." While we currently do not know why and how algae appear/persists but there exists a clear correlation: healthy plants => less algae. So the cheapest and most effective method of algae control is to grow healthy plants. You cannot be a successful aquarist w/o realizing this IMO.

 

[cS]

Hello Jeff,

I apologize for not making my post any clearer. I was not advocating H2O2 as an algae CONTROL device. It is meant to KILL everything at a safer & more convenient level than BLEACH. I made it a point to emphasize that fact. After such, I wrote again that please do not misunderstand that I am suggesting folks to add H2O2 as a continuous method to control algae. Even after that, I quoted you and emphasize further that healthy plants => less algae; and that in the end, it is the best current method for effective algae control. I think I triggered a misunderstanding by quoting only part of your message that is relevant to what I had to respond: H2O2 do suppress algae when added to the water column in large enough quantity. I do not know enough about the reactive nature of radicals so I didn't get into that discussion nor did I quote that portion. :wink:

Let me rephase, why can't I dose small non-lethal levels of H2O2 or ozone to suppress algae? If you have direct evidence for this in a controlled experiment, I'll be more than happy to change my views.

It doesn't Jeff and the lack of "small non-lethal levels of H2O2" in your previous post is where I misunderstood you. Apologies.