Well I'm guessing your having trouble with the purple spectrumed aquarium lights. well it depends on wut lights u keep on, turn the actenic blue tubes off, turn the purple off...if u got metal halides...i think it replicates sunlight really well so the colors look as close to natural as possible. if u want ur marine aquarium to look like u shot it at a reef, try the combo of actinics with a low powered or blue tinted metal halides. IMHO flash is totally not necessary...and if u just have to use it, then bounce it off styrofoam. n oh yeah...best time to photograph an aquarium, a day after ur recommended 30% water change...hehehe...keep em hungry (SPCA this is purely for artistic reasons) N u'll get them staring at the cam...plus since they r hungry...they tend to focus at the camera thinking somethings coming.
I'm no expert at taking photographs at all, but have had aquariums for 20 yrs now...so i guess dat helps.