Julian

I was just wondering if i have about 1.5-2.0 inches of fish per gallon, how much water and how often will i have to change it?

Butterfly

Depends on the fish(some are messier that others) and the size of the tank(larger tanks are easier to keep stable)
Carol

Julian

well its a 20 gallon with 3 swords, 2 mollies, 2 cories, and 1 oto. the cories and the oto hardly make any mess tho

Butterfly

You really aren't over stocked and these aren't heavy waste producers. I would recommend weekly 25% water changes and every other week substrate vacuuming.
Carol

Julian

i know im not over stocked right now but i was thinking of adding some tiger barbs as the tank feels a bit empty. any suggestions as to other fish i could add?

Barbrella

I would not put tiger barbs in there. Too big, too aggressive and you need too many of them.

The only thing I might add are a few more otos, since they very much like company.

Your livebearers put out quite a bit of waste and swordtails grow pretty big, so I think you have enough fish.