Devon Sinsley said:
Well 500 gph I could see
500 gph is going to give you just above a trickle, especially if there is any rise. The most important thing, however, is to get a pump designed for ponds, not a sump pump, they are wildly different. The pond pump is designed for continuous running, the sump pump for intermittent running. The sump pump won’t last a season. Yes, the pond pump is more expensive, but well worth it.