The Blue Stuff Swimming Pool Chemical - 0.9l Qt

With The Blue Stuff, do you have to lower chlorine, etc., before use?

I have a salt pool . Is the purple stuff a stain remover? Do you have to lower the chlorine?

I have a high copper content in my pool water. Will this lower it?

Is there another way to remove the metals from the water, once you remove stains, than having to clean the filter?