T-4 closed loop flow question

[eastcoaster1]

I plan on using a Velocity T-4 (1250 GPH) on a closed loop with a SCWD. I plan on plumbing with 3/4 PVC pipe on the return and there will be lots of 90 degree bends. I figure with the loss of flow from the SCWD and the plumbing and head pressure, I'll only be pushing 900 GPH or so. Does anyone know if a 3/4 inch supply pipe will be enough to feed the pump? I looked around but I couldn't find any calculators for closed loops, only overflows.

Any thoughts or first hand experience with a similar setup?

Thanks