Tank size has nothing to do with effectiveness of hypo. What you have in the tank does. L/R, inverts, L/S, corals anenomes etc. will not survuve 3 weeks of hypo @1.009. I never heard of hypo working @1.015. My guess is that it wouldn't work at that level. Also am not sure that it's a good idea to have fish, inverts etc. @ 1.015 for months. Will let someone else comment on thsi.