Ah, yes. I see your tube and air stone. I can't see the air pump. The little sponge I linked to doesn't have room to add an air stone. You just attach the air line to the sponge. If your air pump is not above the tank, you'll need a check valve on the line, as well. It allows the air to flow only to the tank and prevents water from siphoning out of the tank in the event of a power outage.
Sponges don't need to be cleaned often at all, and you only replace them if they start to fall apart. You want them to grow the nitrifying bacteria that are needed to cycle the tank. If the sponge gets gunky and water flow is reduced, you swish it in some of the tank water that you've removed during a water change, to remove the debris. I've been running that filter for about 10 weeks and am going to do that for the first time at my next water change. Once a month is okay, but may not be necessary.