It's not so much the 4 fish. You probably overfeed. The bacteria in your tank couldn't keep up. I wouldn't keep 4 damsel in a 10 gallon tank. Probably wouldn't keep any. They can be very territorial. They will ever go after your hand when you put it into the tank. When you do add fish don't feed to much. Shrimps abd inverts are better for such s smell tank. Msybe 1 goby too. Just don't feed. You can buy water at lfs. Just make sure they don't charge you more than 1 dollar a gallon for fresh water. You can buy distilled water at supermarket for .69 cents a gallon
