i used baquacil for many years. I want to switch to chorine now that it's a new year. i haven't used any chemicals since last august. I live in Maine. Should i change the sand before I start, or is there residual from previous years in filter?We have been dealing with iron staining in our in-ground pool since last season. We know it's iron because we have been able to completely get rid of the stain by circulating ascorbic acid. However, the iron eventually settles back onto our steps and liner in the form of a brown stain. We went around in circles with that a few times last season before we drained the pool and closed it for the winter. At the beginning of this season, we determined our shallow well (which is what we use to fill the pool) had excessive iron and some sort of bacteria. We pumped out the well, scrubbed down the walls and bleached it. We then started to fill our pool, and the staining started again. My husband determined that the holding tank for the well is rusting out on the inside. We are hoping that this is the cause for the excessive iron. What I am wondering is, what is the best way to get rid of the iron already in our pool? The water level is just below the second step. Do we need to pump most of the water out? Or if we just go ahead and fill it the rest of the way with a new source of water, will the iron be diluted to a point where we can use AA to get rid of the stain and use metal out to keep the iron in solution?