On shallow sand beds I like to gravel vac them on every water change. On "true" deep sand beds, as in done properly, the sand bed should not be disturbed (that includes digging fish). Personally, I like to replace the sand bed every 2-4 years. It can be removed, bleached, then dried out (this will off-gas the bleach). Then I "cook" it like with live rock, basically just letting it sit in a bucket of RO water giving it a stir once a day, then draining the water every couple days. This will leech off the phosphate. Then the sand can be used and will be better than new.
