After draining 1/3 of the pool and refilling (twice!) we still only got the cya level down to 76. With the FC down to 0 we used a stain out product and then a metal out product. The pool looked great...until we added chlorine back in...now all surfaces are stained again. This is the 2nd time we have done this whole process and while the copper has gone down from .4 to .1 we still can't seem to get it out. The stain out and metal out are pretty expensive and we don't want to keep having to use them. Our public water has no copper in it...we think it must have come from algecide that the pool openers used. How can we get better results that will last? Can we ever totally remove the copper...or will we eventually have to drain the entire pool? We feel like we are going to be battling this forever and we don't want to keep throwing $90+ away everytime we try to treat the problem. Any advice would be appreciated, thanks!!!

-16,000 gallon inground pool, with vinyl liner & sand filter