I had the top of my fibreglasss pool sanded and recoated with gelcoat. It really made a mess - I skimmed off most of what I could and put a stocking leg around the skimmer basket. Some got through to the filter. I haven't noticed any sighns of anything wrong with the sand or filter. I did backwash a lot when it was first finished. Lots of white stuff came out. I think you will be fine. The water was cloudy at first - I shocked the pool for a couple of days.