Very Interesting Problem

[CarlD]

Hmm...


See I originally thought it was the CYA also. However, these are all happening on pools that are being opened for the first time this season. We check their stabilizer every year because we drain our pools half in the winter. They all have very low stabilizer from the loss of water. So that means the too high CYA level is not the problem. As for our strips, the FC and the TC are the levels we are looking at for this problem. When this problem occurrs, its never on the slightest of hugh difference. Its always a major difference and definitely noticable every time. Large amount of TC, and no FC, any more chlorine added doesnt show up until a break point shock.

I suggest you stop using strips and go to drop testing kits, and get one with FAS-DPD powder testing of chlorine. You will get more precise and reliable results. TC and FC tabs on strips rarely match up correctly. Since TC = FC + CC, you will be better off getting a direct CC reading from FAS-DPD.

The tabs for CYA, CH, and pH are nearly unreadable on strips--so much so I consider them nearly worthless. But drop testing, again, will give a much better read.

CYA should not drop so much unless the water has lots of contaminants that metabolized it. Draining is simple: Drain half your water and refill and CYA will be cut in half. If it was high, like 100ppm, then replacing half the water takes it to 50--a high but reasonable figure.