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2-3 times a year if you don't have fine polishing pads inside that will plug it. I have an FX5 on my oscar tank and when I do take it apart it's surprisingly clean. I monitor my water parameters religiously and have no problems.
I have the 206 running a saltwater reef system. I have over 20 lbs of live rock to help replace biomax ceramics. The polishing pad gets clogged monthly is the only thing I really noticed.