i have a 65 gallon with cichlids, danio (giant danios) and bottom feeders. it depends on what cichlids your getting. african cichlids need a much higher ph than other fish, so cories and ottos cant be with them. south american cichlids, however, can be kept with other fish. if you have peaceful-semi aggressive cichlids, i suggest loaches of some sort, maybe yoyo's. they arent algae eaters, but loaches are good fish. a pleco would also do good. maybe a red tail black shark. remember, you would need a big tank (29 gallon+) to have these fish together anyway, so it doesnt look like you could really combind the fish together if your planning to put these fish in your 20 gallon, unless there arent too many fish in there now.