litre tank? i have a comet gold fish named dennis (had 2, it committed suicide), anyways, i was thinking of getting a kind of catfish to put in there with him and another gold fish. can u help me??
Get the goldfish out of that tank. Its less than 5 gallons. Seriously. They get too large for a tank that small. Catfish. No. Your tank is already overstocked. Goldfish get over a foot long. And the smallest catfish would be pygmy cory catfish. But other those those, the next smallest would be 4 inches, then 6, alot of them get over a foot also... Get a larger tank if you want to keep fish like that.
If you want to use that small tank you can add 4 harlequin rasboras and a betta but don't add them all at once add the 2 at a time. You might even want to add some aquarium plants and a 25 watt heater
You should look into getting the proper housing for your current fish before getting another fish. A common goldfish needs 20 gallons at least and will eventually need 50 gallons because they get to be 12+inches long. Also, commons should only be housed with commons. The best tankmates for goldfish are other goldfish. Some plecos are acceptable like the bristlenose, but no common plecos! Common plecos like to suck on your goldfish's mucus coating and will cause sores and infection.