One of the most difficult things to photograph is fish in tank. There is often very little light, and on top of that, they move VERY quickly, so even with a REALLY fast lens you are going to have a hard time getting a sharp shot. Using high ISO is a bandaid, but “under water” photos come out very noisy with fish and coral, but fear not….there is an awesome trick to getting that perfect shot, and all you need is the piece of plastic you probably usually leave at home. All you need is a flat tipped lens hood. Put the flash (needs to be a hotshoe unit) to maximum power, and press the lens hood firmly against the glass (thus not allowing any light to spill in from the sides) and the results are spectacular!