We run a bio-wheel type filter on all of our tanks. We rinse our filters under the kitchen faucet every day. When we get the taank overcrowded the filters don’t last as long. Also, adding an undergravel filter will help a lot. You will only need to clean this once a year.

My favorite filter is the magnum 350 canister filter. It rocks. But you have to adjust the water flow for a 20 gallon. (it has a strong current) Usually they are for larger tanks, but I have used it on a 20 gallon as well, just as long as you can adjust it enough. Otherwise, if your whisper and other filter get clogged too often, it may be becasue you feed your fish too much. Excess food will clog up filters real fast. Another option is a larger waterfall type filter. They have the big double ones, like the Millenium and the penguin brands.

There is a brand out there called Eclipse filters
They seem to work best buy the whole Eclipse hood filter.
That’s what we have on are 20 gallon and 2 on are 80 gallon
they really are the best

cleaning the tank or changing water should take place every month specially when you have two filters.
but if you are still cleaning alot.
consider to feed your fishes just enough they could eat. overfeeding makes your tank dirty by the fishes excretions and uneaten food.