Dude. Why are you having so much trouble? I have a 125 gal salt & 45 gal fresh. I have some fish in my tanks going on 8 years now. You really need to go to a 'fish' place & not some box store like Pet Smart or Pet Co. They have no clue what there talking about. What kind of fish are we talking here? Tetras? Barbs? Cichlids? Guppies?