Yesterday we tested our spa FC to be 25! Strange thing is we had not added any chlorine to the spa to cause this rise. Today we retested the water after leaving the lid open all night and found the FC to be above 30 by then I had just stopped adding drops.No chlorine had been added? I just dont know what is going on to cause this. Any ideas? Im thinking of draining and starting over but sure would like to understand what is going on here.