Black stains on bottom near drain

Stains on the pool surfaces, pool equipment
or on the swimmers, or off-color swimming pool
water. Discolored but clear pool water.
dickwms

Black stains on bottom near drain

Postby dickwms » Wed 31 Aug, 2011 12:35

My in-ground pool has white plaster which has a black circular stain next to the drain. It is obviously the lowest part of the pool, where heavier liquid, like liquid chlorine, would collect. The SS brush doesn't phase it. Latest water analysis shows pH 7.4, total alkalinity 100, cyanuric acid 70, total dissolved solids 1800, and no phosphates. I use liquid chlorine. Previously I used pellets in a floater, but cyanuric acid went high, and pH went low. Comments, anyone?


dickwms

Black stains on bottom near drain

Postby dickwms » Tue 19 Mar, 2013 12:50

Just for the record: I tried 1/2 gallon of Muriatic acid poured through a pvc pipe to arrive at the stain without major dilution. It formed a heavy pool at the black stain. The stain was gone in a few minutes, except a bit around the edges. At the point that the heavy pool of acid went into the drain, a stream of bubbles indicated an undesired attack, so I started the pump, pulled water through the drain line, and also used the brush to disperse the concentration.

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