I just got done testing my chemical levels and noticed something unexpected. I've never encountered this issue and I am confused about it. The following are my current test levels (HTH 6-test tester):
FC = 4
pH = 7.5 (currently aerating to raise to about 7.6 or so)
TA = 100
CYA = 40
CH = did not read any hardness (indicator turned yellow after swirling in the test container)
The CH is what is causing me headaches. Last week it read 200. It has stayed around 200-240 all season. Now all of a sudden I am not getting a reading from the indicator. One week ago I put some calcium chloride (from Poolife) in the water because I wanted to raise the CH to about 250. Today, nothing.
Any thoughts? BTW, this is a pop-up pool with a vinyl liner. Should I be concerned? I read somewhere that CH is not important with a vinyl liner. However, I had never heard this before reading about it recently. I have been operating under the assumption that CH should be kept between 200-400 (from The Pool Calculator).
The only other possible relevant factor is that I have been actively lowering TA over the last couple weeks. So I have been reducing pH to about 7.2 with pH Minus and then aerating to raise pH back to about 7.6-7.8. I am pleased with the pH and TA levels now. I don't know if the pH Minus has had some kind of a reaction on the water's hardness. It has never been an issue before, but I thought I would mention it.