I use a Fish Mate UV & Bio POnd External Filter. I have a 1000 gal pond outside and a small 60 gal. inside. They come in all sizes, and if you order from Doctors Foster and Smith, they will reccomend the size pump for your filter. Mine works great, and the water is always clear. I have a Eastern Painted and Southern Painted in the 60 gal inside. This summer they will go in the big pond as they are getting bigger. Just remember to double the size of the pond when ordering the pump and filter, because it is for turtles which need a higher filtration.