Have any of you had to deal with biofilm in a swim spa? We have a customer that has to order his water and is trying to save the batch of water that he has in his swim spa now. Unfortunately, he has let biofilm start growing. Normally, in a regular tub, we would tell them to just superchlorinate then drain, but he is trying to avoid that. Our next suggestion would be to get the chlorine level up to 10ppm and keep it there for a week or two, and hope that destroys the biofilm. Has anyone tried that and had success or failure with it?