We have a 20 year old community inground pool and spa at our condo complex. It is a concrete pool and it uses Chlorine. Every 2 to 3 weeks there is a buildup of a black carbon like substance that forms on All the stainless steel components below the Waterline. Ladders, Railings and Lights. We clean it off with a rag and diatomaceous earth.
We hired an electrical contractor to check the Bonding and they said everything is properly bonded.
The problem is worse in the Spa. The spa is not directly connected to the pool.
