I missed the post about changing the impeller - that would work. I don't know if it's available for your pump but you could go down to 3/4 or 1/2 hp.
I think you could also throttle the flow with the suction side valve if that valve can be partly closed. You'll need to listen carefully for cavitation as the pressure on the suction side of the impeller gets lower and lower.
If the pressure is 17 on recirculate, what is it on filter?
After you get a little clearer - or kill the green, you might try to put a little DE in the skimmer and watch for it to come out the return. If it doesn't, you could try putting enough DE in to raise the filter pressure by 1lb. This can help filter finer particles. This should probably done in conjuction with getting your flowrate through the filter down. Probably want to wait on the DE till the green is gone.