With these small pumps a lot depends on the height you are pumping the water too, if your pool were on a hill and your hose ran down hill to its ultimate destination, they act as sort of a powered siphon , on the other hand if pumping up to ground level they will start off ok, and get slower and slower as the water level drops. Reviewing a couple of typical 1/3 HP models, show published flow curves of around 50 gpm at 0 ft head, 42gpm at 5 ft head, and around 32 gpm at 10 ft head.
Ike
p.s. hose size may effect back pressure here, typical hoses range from 1/2 inch for cheap hoses, 5/8 inch for most better consumer hoses, and 3/4 inch for high quality contractor grade hoses. At any given pressure a 3/4 inch hose will flow about twice as much water as a 1/2 inch. In the real world the shorter and larger diameter the hose the better, with a 50 ft 3/4 inch hose you would likely get around 20-25 gpm in the real world, with a 1/2 inch hose those numbers drop considerably, likely below 10 gpm
