I have done 2 tanks with water in it and fish, corals, and invertebrates. Just put saran wrap tight over the lid. Takes about 40m per coat with that paint. Run a fan on it. 5hrs it will be done. Black will pop the colors in the tank better.Yea I was wondering if I could paint with water in it but I'm definitely going black. And more rock is coming. Probably stay at 20 thought I don't want it to look too cluttered