Hydrogen peroxide disaster

[_Maq_]

Could be the plants melting, but it is likely to be that the lower plant mass isn't using as much of the fertiliser as well.

I think it's the result of oxidizing of lots of organic matter. Unlike much of organic matter, the oxidized species are largely in ionic form, thus increasing conductivity.

If you regularly poisened your dog /cat the rspca would have you in trouble with the law.

Hydrogen peroxide, like virtually ALL substances, is dangerous above certain level.
Speaking about the trouble with the law: What do you think, in aquarium hobby, is hydrogen peroxide killing more fish than carbon dioxide injection? I doubt it very much.