I would go with an external pump if possible. They are quieter, last longer, and transfer less heat to the water. 900 gph
is not enough flow for a 130 gal
reef tank. It's enough going through the sump I think, but you need more flow in the main tank. I would go with a closed loop pump system using a SQWD or at least multiple returns. Powerheads clutter the tank, require cleaning, add heat to the water, and usually don't last nearly as long as a good external pump. You really should have at least another 1200-1500 gph
flow in this tank. Examples of pumps you could use are an Iwaki 30 RLXT for the sump return and an Iwaki 40 RLXT for a closed loop. Remember that the pump isn't going to pump what it's rated. Most pumps are rated at 0' (some are rated at 4') head. By the time you pump the water up to the tank and figure the frictional losses from elbows and such, your pump output will be decreased somewhat. If you slightly oversize the pump, you can always choke it back some with a valve on the PRESSURE side...never on the suction side.