I have a 1.5 hp pump on an 18' AG pool. Yes, it is too big, but that's the only pump the store offered with the package that was 2-speed.
I plumbed it with 2 inch PVC and installed a flow gauge as well. I wanted to see if I could possibly downsize the motor down the line.
low speed - 1.7 psi @ 28-29gpm <---(Would this be enough for normal use?)
high speed - 11-12 psi @ 78-80gpm
The high speed blew off one of the pvc connections. Wow, what a water flow coming out of that pipe at full speed! YEEHAWWW!! I just reglued it, but was afraid to turn it on high speed again. I wanted to run the pump for a couple of days straight, but with this blowout AND another very small drip on one of the fittings, I'll keep it on low for now and overnight. The other fitting isn't easily fixed. ARGGGHH!
My gauge only goes from 20-70 gpm. I thought I would just barely fit into that range, but apparently not. No big deal. I'm hoping to never really use high speed, especially with the Pool Rover Jr. cleaning.
Oh yeah, the pool water turns like a freaking toilet bowl flushing! Wow. I think the kids would get swept up in the circular motion and go in circles from the force of the water.