Ph Test goes from 7.6 to purple quickly

RDN

Silver Supporter
Jun 3, 2011
21
Bellevue WA
Pool Size
21000
Surface
Vinyl
Chlorine
Liquid Chlorine
Hi, I've got a situation I've never seen in the 30+ years of pool ownership.

When I test the Ph, it initially looks fine (~7.6). But then, after about 30 seconds, it turns deep purple.

The Free Chlorine is about 4.4, CC is about 0.4. Water temp is 52.0 degrees F.

Should I be concerned? The Ph has been fairly stable, trending slightly upwards, so I've added a little muriatic acid the past couple of weeks, but not much (like 4 ounces at a time).

Ron
 
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