Unfortunately every time you shock the spa it will oxidize the metal in the water and force it out of solution. I would check your shell next time you drain and refill, as it might have a slight stain to it from the copper.
A Good trick is to add about 4-6ounces of metal control while you are filling your tub, and then wait atleast 48 hours BEFORE adding any shock or balancers. Also after this period of time bring a sample to your dealer for testing and have them test for copper to see if you got all of the copper out of the tub.
Another suggestion is purchasing a spare set of filters. Use one set for your refill, and once you have all of the copper removed from the water put the second set of filters in. Deep clean the "fill" set of filters to remove any copper from them. This way they will be ready when it is time to swap out your filters.
What very well could have happened is your metal remover did in fact remove the copper from the water but after you shocked the spa with chlorine it caused a chemical reaction and the copper was brought back into the spa via the filters. This is a common occurence in pools where customers have damaged a heater due to improper water chemistry, done a metal removing treatment and shocked the pool BEFORE having the filter properly cleaned. Just some thoughts.
Jason,
Store Manager for a D-1 & Caldera Dealer
