Recommended Filters for Goldfish Tanks: Use a spraybar to diffuse the flow & add oxygen. Rena Filstar XP, Fluval FX5, Magnum 350, Eheim 2080, Eheim 2217/2211 (super quiet!), Fluval 205 (quiet), Eheims are the quietest (classics quieter than pros): Getting "EHEIM Classic External Canister Filter with Media (2213 up to 66 gallons)" $90. Get a filter rated for DOUBLE the tank size since goldfish produce so much waste.
A Skippy diy bio-filter, built using a "Rubbermaid" water tank. This has been the most insightful site on my new pond design. I must add that my brain hurts from all the equations and endless options to consider for a well balanced pond. A must read for all ponders exspecially the do it yourselfers!!
A biofilter is a key component for success with your aquaponics system. The secret to a phenomenal aquaponic system is creating a colony of helpful bacteria that help eliminate the ammonia that is harmful to fish and convert it to nitrates that create a healthy system for the plants to thrive. A biofilter helps make this happen.