caution / concern on my part from past trials.
1 US tablespoon = 14.7867648 ml
Recommended here is 4tbs/10g or 6ml/g
This is a valid concern. Some thoughts on it:
With vigorous flow, the H2O2 concentration does not remain at the initial dose for the entire treatment time. It will be reduced not just in reaction with algae, but also quite rapidly at first in easier reactions with omnipresent bacterial films and organic wastes. So this cannot be compared exactly to a medicinal dip, or any H2O2 treatment where little or no flow is present.
Because of this, in a tank with good flow, the dosage has an exponential rather than a linear effect. Too small a dose, and it will be so rapidly consumed that it has little effect on algae. Too large a dose, and after easily reacted materials are depleted, the concentration stays high enough for the remaining time that fauna may be adversely affected. Tricky, eh?
I've tried many different dosages and treatment times, and I believe my recommendations to be the "sweet spot".
Increase to 6 tbsp./10G for 30 minutes caused lethargy and hanging around the surface in some fish, though there were no deaths and all symptoms disappeared within a day.
Except for the above increased dose, I've had no problems with my golden and weather loach, which I didn't think to mention in my original post because I don't consider them particularly H2O2 sensitive. The crazy things insist on playing in H2O2 spot treatments, seemingly without harm!
Still, if anyone prefers or feels more comfortable with a lower dose, by all means use it. The effectiveness will be somewhat reduced in my experience, but still adequate for anything but tough algae. The efficacy of this treatment is not due only to higher H2O2 dosage, but to good flow and combination with Excel.