All depends on the filtration, circulation and the occupants really. I tend to actually vac about once every 3 months or so. Many say to do it once per week.
If you have snails, apple snails etc, you will need to hoover more often as snails are quite the little poo machines , maybe that's why you've heard 2-3 times a week. But as andywg was saying, depends on occupants and filters n stuff. I do mine once a week with the water change. I've moved my snails to their own tank. Cheers Xanthe
also on the physical size of tank as waste builds up to "toxic" levels far faster in a smaller volume of water then a larger hence why i end up doing mine 1-2 every week or so
WHOA I just did a 50% water change along with a gravel cleaning and damn did my 42g have alot of junk in it!!! It was the first time in like 5 months so meh... Never gona let that happen again.
My uncle doesn't clean his either...guess he lets the plants do it, but his gravel is as black as charcoal and it wasn't that way in the beginning. I'm not saying your substrate is black, how would I know?... just saying that my uncle's is and it is terrible!