For a goldfish tank, what have you found to be the best filtration system? By "best," I mean most efficient at converting ammonia, but also easy to maintain. An HOB [hang-on-back] filter A canister filter ______________________________________ Please elaborate on brands, pros & cons -- basically, anything that will help me make a decision. I will be housing one goldfish that's about 4" long [body length] on a permanent basis. He is a "special needs" goldfish that needs to be out of the pond. Going to start out using my 20 gal tank, but will go bigger if necessary. Thanks for your help!