Use one sump solely for bio-filtration, and run 200-300 GPH through it. Then max out the other sump for mechanical filtration. High flow rates are simply not optimal for the biological bacteria habitat. In fact, every successful nitrate reducing contraption requires a really, really low flow rate.
I used a food-safe (white) 55G can for my 125G main tank. You can find food safe materials by doing a Google search for "Restaurant Supply" in your area. My Sump:
1. Water flows into about 6L of pillow stuffing for mechanical filtration ~300GPH.
2. The Laguna Power Jet 2000 pump puts ~100GPH through 4L of submerged Matrix/Pond Matrix and;
3. ~300GPH back into the main tank.
4. Drip system puts ~5-10 gallons per day in;
5. Excess water is drained into sewer.
I haven’t had a NitrAte test read greater than zero since my tank finished cycling more than a year ago. My Ammonia and NitrIte readings have also remained 0. My healthy fish can be viewed here: http://www.monsterfishkeepers.com/forums/showthread.php?528193-Green-Terrors-are-almost-here!
You NEED to study the Herbie Overflow (Sp?). The system you're developing will be loud without it.
