Clean the exterior of the aquarium glass with distilled white vinegar (it's not toxic to aquatic life) before photographing.
The spots are actually from small particulates in the water, and look obnoxious when the flash goes off. So i must have forgotten to clonestamp those out.
I see. Some of the spots in the catfish photos look like spots on the exterior of the glass.
Also, one way to remove so much floating particles in the tank is to add poly-fil (
not the type that is flame retardant) to your filter. The poly fibers "polish" the water and remove them. When I had my freshwater planted tanks, I used this in my Eheim canister filters, and it never failed to keep the water almost crystal-clear.
Have you heard of a guy that goes by AQUASUR (I believe that's the way it's spelled)? He's on one of the aquarium forums I frequent and also on a couple of the more popular aquarium forums. He has AMAZING aquarium photography, and he will answer questions on his method.