I have a 90 gallons tank and using a rio 20hf for return pump. I'm running two 3/4 return. Is this pump is too much for this tank? my tank have a build in 1 1/4 drain. I can't seem to open the return valves full flow. Right now, I have to turn the output valves to half flow. If I open the return more than half, I have a lot of rushing water flow coming ddown the drain. Let me know what I can do to improve this. Thanks.