It's not a problem for your sand filter. There is the possibility of some wear with a cartridge filter which is why I don't pour it in the skimmer in my own pool, but I'm being conservative. Unlike pouring acid in a skimmer, which is an absolute no-no, I don't think there's ever been a report of problems pouring chlorine through the skimmer -- again, I'm just being conservative by pouring it over a return flow at the deep end.

Richard