I have a 40G FOWLR tank. Right now, it contains 1xClown, 1xChromis, 2xRed Leg Hermit Crab, 2xBlue Leg Hermit Crab. I will add 1 more clown, and either 1 or 2 Chromis. That will probably be all the livestock in there. My water changes are not that big, however, I want to invest into RO/DI unit...