Stumpy,
I only do a partial water change once a week. I have a Fluval u2 mounted on the side, and it does most of the cleaning for me.
The water area in my tank is somewhere between 5-7 gallons, and has lots of hiding spots for fish. My frog doesn't eat in the water. Usually just soaks while sitting on top of the filter. The red is circling the filter in the back. My frog sits on it and the rest of the water area basically goes completely unused.