What GPM should I aim for in a 20,000-gallon pool pump?

Aim for 40 to 50 GPM. That’s based on turning over the pool once every 8 hours (20,000 ÷ 8 = 2,500 GPH ≈ 42 GPM). For a faster 6-hour turnover, you’d need about 56 GPM, but most residential pools are fine in the 40–50 GPM range. Don’t oversize the pump — it wastes electricity and stresses the filter. A variable-speed pump is worth the extra cost.