If you can't get the Rena's to work, eheims are nice as well as the Fluval FX5. The FX5 can filter A LOT of waste out before they slow down and they are a very user friendly filter. I ran them on my fish tanks for years along with a sump with no problems. The FX5 is a lot easier on the wallet as well....$210 on Amazon.com with free shipping.