You can test with a vitamin C (ascorbic acid) tablet -- it will usually lift (re-dissolve) copper or iron. You'll need to let your chlorine drop to, say, 10 ppm before you try that, though. Chlorine destroys ascorbic acid.

That's OK, though. There's no reason to have FC = 35, unless you have some algae. (If you do, brush at it, and it will probably be gone by the them chlorine levels drop.