That would be about what I'm left with or maybe sligthly less. I can't use any H2O2 product now as I have started with the Canna Boost which arrived today. It has a warning not to use H2O2, I think because it already contains it maybe. I haven't ever seen algae build up in my tank, but I reckoned that was because I sealed it from light & have an air pump in it. It has always been completely changed at max every 10 days so not sure how it will play with old water.