I have an AG pool and a sand filter. Got it last May and have only used BBB. I did notice on a paper from the store where I bought the pool that they say the filter should be cleaned with some sort of chemical twice per year - once before closing and again around July. Do any of you go through any sort of filter cleaning process or is that only necessary if you use other products to maintain the pool? I have heard that Baquacil will gunk up the sand in the filter over time and this particular store really pushes Baquacil.