The sanitizer is iodophor. The condition is water with high pH. If your pH is greater than 9, iodophor may not be effective in the recommended dosage. At that pH, the amber color will not be present and rather than kill the little beasties, it may become a breeding ground for them. The solution to this beastly problem is to either lower the pH of the water or increase the amount of iodophor until the amber color is achieved. Lowering the pH even of large amounts of water can be accomplished via the addition of a small amount of acid.
Some brewers think that phosphoric acid is the best for the job.
I prefer to use an organic acid that isn't so corrosive, such as tartaric, malic or citric acid. The choice is yours. I've most always used the color of the water to determine when I have added enough Iodophor because at my advanced age it's easier to see color density in five gallons of water than it is those little lines on the iodophor bottles. Anyway, a great big thanks to our Florida customer who brought this to our attention. The place was really big and open, but you could sit at your table and not hear the people next to you.