If that's before head loss then you are probably only seeing about 200-300gph, depending on how good the pump is. That is only turning your tank over through the filter about 1X per hour. I think you need to get a larger pump or more pumps to increase that to about 5-6X per hour. With that, you can probably get rid of all three of the power heads.
For example, my 220 will be running through a 55gal sump, for a total of 275gal system. Now, the way tanks are measured and since the sump won't be filled completely to the top, so I decreased my system gallons to an estimated 250 gallons. To get the total turnover rate I multiplied that 250 gallons by 6X for a total turnover of 1,500gph. I decided to go with the Rio 20HF pump because at 4-5' head height the pump is capable of flowing 800-900gph. With this, I can install hand valves on the pumps to throttle them back a little bit, if I need to.
I think you need to increase the flow through your sump and do away with the power heads, but wait for others' responses because there may be some differing opinions.