The light is PERFECT on the 20 gallonH, however we have one on a 20 "tall" which is really 25 gallons and the light doesnt get down to the bottom quite as well.
I even had an anenome doing great until it became stubborn and stuffed itself in a crack under the rock and wont come out to find the light. I feed it but its still slowly bleaching.... stupid thing.
I'll post more updated pics soon
-Diana