Thanks Peathen.
I am only using one flash at present though I do want another. I want to light up both sides of the fish but I think a quality lens is next on the list first. The flash is a Canon 430EX II speedlite in conjunction with a Glanz trigger. I have it sitting on the lid, facing straight down and about 7" back from the front of the tank. The tank is 40" high and 48" front to back so there is plenty of room to drown out the background. I try to get the subject when it is off to the side of the flash. I have about a 1.5' range either side of the flash to shoot in. I just need the fish on the right angle. I hope that makes some sense.