I have a 20 gallon reef that also uses a Fluval 404. I don't have a sump or refugium or skimmer either. The Fluval is empty of all media and I clean it religiously. Since my tank is so small, the Fluval makes water changes a breeze. The Fluval holds about 3 gallons of water. I therefore do a 3 gallon water change every 5 days. I simply disconnect the filter via the stop valve, take it to the bathtub, dump out the 3 gallons of water, rinse all parts of any detritus, and reconnect the hoses. I then let the Fluval fill up again, thereby draining the tank of 3 gallons of water, which I replace with new saltwater.
This tank has been successful for over a year.