I do water changes about every ten days. I have a ten gallon with two clowns, one cardinal and about half dozen hermits and snails. I clean roughly half the sand bed at a time in a checkerboard pattern. Looking at a checkerboard you have red squares and black squares, you'd only clean the "red squares". By cleaning this way you leave an even amount of bacteria on the sea floor for your tank to mature. About every three water changes or once a month I'll just let the water evaporate and add some RO water back in with no filtering of the sand. If you do this remember that you don't want to replace salt water with more salt water or your alkalinity will spike. Salt does not evaporate, replacing with RO water helps keep it in check.
