I think you could pull off 4 geos, 2 sev, 4 keyholes & a dozen corys in a 125 with no problem. The thank is underfiltered IMO and will require twice weekly water changes. If going the HOB route 2 AC110's would be a better fit. Then down the road use the 2 AC70's on the 90. I use PFS with my geos. I was never fond of black sand but you could mix 25% black with 75% PFS for a nice look. Anyway it's your tank you have to look at it so use what you like. GL & post some pics when you get it up and running.



