Off the Chart Cyanuric Acid

[BnaRealtor]

Tested FC again this morning before the sun was up. 13.5 ppm. A 2.0 drop overnight.

[PoolDoc]

Not huge; depending on whether you've been using the pool, or had a bunch of rain, could be normal. Or, with the chlorine up, you could be cleaning up debris somewhere.

But, check corners and crannies for algae or slime. And, keep your chlorine up (15 ppm) up for several days, and see if the overnight loss drops.