most pool filters are just fine for mechanical filtration but you need to add some bio-capacity in the form of a tub of bio-balls...scrubbies....ect. after the main filter.
Get a small bead filter designed for koi pond.They won't clog up with a fish load like a swimming pool filter will.They are easy to backwash and can carry a large fish load for their size. There are many brands and sizes and all work pretty well.