I have a Fluval 304 cannister on my 29 gal
, and I've been very happy with it. It's on sale at Big Als online for $73, including the media. I have tiger barbs and rasboras - they enjoy the 304's current, but are not at all knocked around by it. The Fluvals also allow you to adjust the outflow by as much as 50%.
If and when you get that 125 gal
, you could buy a SECOND Fluval 304 and run both on it.