I was thinking this too, but OP raised the tank water level and reported that sump water level didn't change. From this I took that OP 1) does not have air in the drain lines and 2) the drains are not meeting the demands of the pumps, whatever the GPH is. Given that I don't see any valves on the drains my conclusion #1 above may be incorrect. Good catchAre all 3 drains running full siphon?