CRIZAL: Firstly, welcome to the form. Secondly, thank you for SHMBO, because I always stated: "the Woman who must be obeyed" which does not easily reduce down to an acronym! With respect to your question about external filters, there are tons of same available. They are usually referred to as "canister" filters. Google "canister" filters, and up will come a zillion, such as "Fluval", "PennPlax," "Marineland", and on and on! None of which are cheap, particularly for a 20 gallon water feature, BUT, ease of use is always important! Incidentally, in the external canister pump, which never makes direct contact with the water feature water, the Pump and the Filter, are both contained in the one external unit. Take it from me. Amongst my numerous Marketing adventures, many, many years ago, and with a regular job at the time, I opened up a "Pet Stuff" location, and then another, sold thousands of dollars worth of tropical/salt water fish and aquarium equipment. It was a whirl! Cheers!