If they are Tapajos how fine things are going to be will be largely dependent on the sex ratio of the group. A 48x12" footprint doesn't allow a whole lot of space or breeding territory between males.
Sorry yes these. They are about 4-4.5" not not including streamers....which they have none becasue I have them in a 90 tall with a constantly spawning pair of wild sevrums. I have a 55 needing some fish in it in one of my offices and I thought a school of the geos on the bottom and rainbows on the top would be nice if it would work. Not sure of the sex ratio really...might be 4m 3f which I know wouldnt be too great. I am not opposed to pulling some from the group if it didnt work or if some spawning happened and all hell broke out. They have grown up together and been good to each other so far...just the severams spawn so often they are always in the top of the tank. Filtration now is 2 AC70's with sponge and bio only (on the 55 in question) and waterchances about every other week....might move to 2 eheim 2017's or some other kind of canisters I have laying around. Deco would be pretty open just 2 groups of plants on each end....I just wanted to get opinions....