i have a great Hayward C2030 pool filter, I used it several years on my small koi pond. It had the water crystal clear. The problem was the fish waste and plant roots kept clogging the filters up,. once a week I would have to take them out and hose them off. I finally got a real koi pond filter system. I cleaned the Hayward up and its ready to filter after plumbed and new filters installed. Hayward filters CX481XREPAK4 replaces PA57L. but I always used GUARDIAN POOL FILTERS, MADE IN PA. 717-146-04 in a four pack.