You need to have one tank higher than the other. You would need to drill this higher tank so it can drain into the lower tank, preferably with a herbie or bean animal (but a durso will do the trick also). The return pump in the lower tank would then feed the higher tank. Only one pump.
A sump doesnt need to be below the display, just lower than it. My current build has the sump next to the display and approximately 12 inches lower.
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