I have used both sequasol and metal free. They are both good, so it doesn't matter which you use. I would add a good dose right after your fill - a little more than the bottle says. You will not have to do anything else when you close. I have already closed with stains and opened to a stain free pool - I don't know why, I can only guess, so don't worry about adding any sequesterer when you close. I would save the chemicals for next year when you open. Next year when you open, before putting anything else in the water add the sequesterer. This way any metals the were introduced over the winter or with your fill water will be taken care of. Then you only need to add it if you see any stain starting to form. If you see stain start, take your ph down to 7 - 7.2 and add sequesterer - it should lift the stains before they settle. Feel free to ask any questions you have