4 glowlights 4 regular neons they will scool together it would look super cool...maby 6 bloodfin tetras pictures online dont do them justice the fins get realy dark red when in soft water and maby 4 marble hatchet fish if you have floating plants and a lid, 1-2 small angels to make them school a 20 galon is big enough for all of those fish and if your planted tank has a larger bushy plant like java or xmas moss penguin tetras are realy cool the larger ones have a realy long bottom tail fin and they kinda point out of the ball like they are on gaurd duty..but just off the top of my head some good comunity soft water fish are: kerri tetras, flame tetras, cochu's blue tetra, ruby tetra, gouramis any that catch you eye, killifish/splash tetra they can come in some realy cool coulours, a betas do realy good in softer water, clown or kuli loaches.... hope this gives you some ideas but remeber you have to have a "larger" fish then the tetras like an angel to make them school or shoal a couple 2" angels would do the trick...remeber some of these fish may be hard to find but would be well worth looking around for
they are cool
