If you want to do it properly...
Take pics in RAW mode (get a camera decent enough to do that), then adjust the white balance on the computer to match your tank (be honest!)
Otherwise... the big thing, find the white balance on your camera, see if you can set it, get a greyscale card ( you can find them to print out on camera sites) and match it to your camera/lighting to get the white balance correct.
Generally white balance is what effects the colour balance, unless you're being bad and playing with exposure (which is generally noticible and only effects brightness, not colour)