To use 1 pump only, you have to site the nexus about 6 inches higher than max pond water level, and return the water via 4 inch pipe under gravity only.
Can’t see the point on a sieve and nexus TBH, especially on a 310 with the eazy lid and overflow pipe, it’s either sieve/bead combo or nexus only IMO.
4600g fibreglassed pond with front window. Covered fish house style. Skimmer and b/d to Oase Drum, into 2 gravity fed showers with C/Bio and lithaqua, 2 pump returns through 2 55w UV’s, 230k H/X, to either underwater return or waterblade. Airtech 80