Black sooty film on pool light rim

I have a very fine, black sooty film on all pool light rims, which I believe are stainless steel and show no sign of corrosion. This film leaves a black mark on a fingertip when touched. It wipes off easily with a cloth, but returns very quickly. I don’t see any black film anywhere else in the pool, but there is no metal in the pool other than the light rims. It doesn’t look like algae to me, but I’m no expert. The pool is salt water clorinated. Any help with eliminating it would be greatly appreciated.

I should add that I’m in Florida and the pool is in commission all year. I’ve searched but haven’t found any other posting about deposits, discoloration, etc. that resemble my black sooty film issue.

That black soot is likely being caused by electrolysis from the salt system. The good news is that there is a simple fix. You can add a sacrificial zinc anode to the pool. The zinc anode will essentially absorb the electrolysis.

We have a zinc anode that can be attached to the light. The part number is 0173-4.

Very good, thank you.

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