Originally Posted by CeeTropical
I looked at the freshwater fish and I like the mollies, swordtail, cichlids, angelfish, sharks(Rainbow shark for example) and rams. Are any of these compatible with each other?
The quick answser, in a 20g, is no. And aside from this, if a larger tank were under consideration, we are back to water parameters being different for some of these so they are not compatible.
From this list, and depending upon your water parameters, a bonded pair of rams would work. There is the common Blue Ram and the Bolivian Ram. The profiles explain the issues with each, and water param requirements.
Depending what "cichlids" may refer to, possibly. A pair or harem of one of the South American dwarf species with some dither fish could work, if you have soft water. A group of "shellies" from the African rift lake cichlids could work in hard water. But nothing else in a 20g from the cichlid group.
A smallo group of mollies if the water is medium hard to hard and basic in pH. Swordtails get too large for a 20g.