I have a 20 gallon tank with 2 mollies, one guppy, a gold algae eater, and 3 snails. The lady at the pet store said I can get more. I want non aggressive, colourful, and medium sized fish. What do you guys recommend?
I would find a bigger tank or rehome the algae eater, that's a gold variety of the Chinese Algae Eater and they get up to a foot long. They're also known to be aggressive.
Afterwards, you could probably add maybe 3-4 more guppies, and another molly, if you'd like to expand the numbers. Or, if you'd like something different, there's lots of possibilities! But first, is your aquarium a 20 gallon high, or a 20 gallon long? That will impact some of the fish you can get. For example, if you still want a bottom feeder once you move the algae eater, and if it's a long tank, you could maybe do some cory cats. I think the regular sized ones might get too big, but I'm not sure. Pygmy cories would be fine though