I don't believe that any sponge filter is rated for a 125 gallon tank. You must mean 125 gal/hr powerhead flow. Personally, I would be running two power filters like the penguin or aqua clears.
The specs say for aquariums up to 125 gallons. Like I just said I run that as precaution against power outages. I was running two HOB units & the sponge and a few weeks ago disconnected one of HOB's as the three filters were a bit overkill for the stocking level I have currently.
• Hydro Sponge Filter #5 PRO
*4" H x 5-3/4" W (Recommended for 40 gal. up to 125 gal flow rates up to 400 gph)
*New high Flow reticulated sponge for higher bio loads that tend to clog regular sponge filters!
*Up to 125 gal. and flow rates up to 700 gph
I based some of my decision off of this guys research and actual real world testing/experience.
Last edited by Elyssa; 02-14-2013 at 08:37 PM.