Got a filter specifically for an 18ft for my 12ft pool £26 pool hoover(they are handy) 16ft tarps to cover it & 2 chlorine tablets floating (when not in use) & goodness I go by if the kids get bloodshot eyes(ill be shot for saying this ) then I take 1 tablet out & bit of fresh water top up never had to change the water all summer in the 4years I've done this