aaronnorth said:Thanks George,
would faster shutter speeds for photographing fished used as they are fast?
This is where full tank shots get tricky, as generally the tank lighting may not be sufficient to give you a fast enough shutter speed. 1/125 sec. is normally enough to freeze most fish.
Cranking up the ISO will help, as you have learnt by now (hopefully), but image grain can be an issue.
Also increasing the aperature will help, but you lose important depth of field, essential for ensuring all the tank is in focus.
This is why flash guns are commonly used by the more serious 'scapers/photographers.
A remote flash is positioned above the tank, sometimes using a light box, to ensure all light goes downwards and into the water. So shutter speed is fast (freeze fish movement), depth of field is good (smaller aperature) and ISO is low (better quality).
My next photography purchase will be a decent flash gun and remote cable. It takes aquatic photography to a new level. All the CAU guys use them, Neil Hepworth, Amano (lots of them!) and a couple of guys on here (Dave Spencer for one).
Another option is to simple get as much light as possible above the tank. I've used 8 x HO T5 + T8s before now.