I used a fluval external canister filter on turtle tank. The canister did a great job cleaning the water (this large red-ear slider produced a lot of ****!!) and has a lot of pressure on the output.

These are meant to be under the tank and they have plenty of pressure to supply a water feature. You just run hosing for both your intake and output, with the output dumping the water at the top. The amount of pressure may actually be too much to dump all of it on the water feature. You can easily remedy that with a T value. One output goes to your water feature and one to main pool. Also, partially close off the line going to your water feature until you have the desired pressure. They're a bit pricey, but something similar should do the trick.

If the parts list comes out cheaper I'll probably make one when I'm ready. If that interests you at all here's a link: HOW TO: DIY Canister Filter - YouTube

RW