I have a 55 Gallon FOWLR tank that i have had set up for around 4 months. I did all the pluming to the sump myself with PVC. My problem is my overflow box can’t keep up with my return pump. If i open the valve on the return pump outlet hose all the way open the water level rises quickly to the top of the tank and will overflow if I were to let it. I only have two elbows in my drain line to the sump. I have been running the tank with the valve about 40% closed on the return pump matching the amount of water that drains to the sumo with the amount of water the pump returns. My overflow box is rated at 800 GPH and my return pump is rated at 700GPH. I’m confused because the head pressure should slow my return pump down even more yet i still have to dial it back. I have the overflow box adjusted all the way down to the lowest water level. Any suggestions I’m ready to add a second overflow box but I really don’t want to or see how I would need to. I just want to be able to run my return pump wide open to maximize the flow rate.