I just take mine off if the wax looks dirty, and no matter how many times I put more on, it comes back off and you find to be slipping a lot. At least once a month.
I do it when the sand starts to bother me and I just let it sit out in the sun and then scrape all of the wax off the board.
i havent changed wax on my one board for maybe 3 years now. looks like it has acme. grip is great tho big bumps ftw