We have a 9 month old fiberglass pool. The pool test shows acceptable levels across the board. We have noticed a bumpy, build up on sides. You can scrape it off with a fingernail, very small and hard. Local pool people can’t identify. Any advice?

Question:

We have a 9 month old fiberglass pool. The pool test shows acceptable levels across the board. We have noticed a bumpy, build up on sides. You can scrape it off with a fingernail, very small and hard. Local pool people can’t identify. Any advice?

Answer:

This could be due to calcium deposits. High levels of calcium can deposit on the walls, especially after extended periods of high pH. You should be able to control this with regular pH monitoring to make sure the pH stays balanced and calcium stays in solution. However, in some rare cases calcium hardness is very high in the source water and alternate water needs to be used or a prefilter treatment of the water done.

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