i've used softswim for several years. the last couple of years we have had pink slime or mold in the pool for a good portion of the summer. it seems to be very hard to get rid of. i am getting ready to uncover pool and am going to switch to chlorine. the pool was drained pretty low for the winter.i have a 21' x 4' round AG pool with a sand filter. i know i need to get new sand for the filter. should i change that before i start adding water to the pool? or should i let filter run for a while first? any idea on how much chlorine i should add to start it up or do i add shock to start it up.