jaymac10 Posted February 12, 2016 Report Share Posted February 12, 2016 Newbie HT user here. I have this coating on the knobs as well as in certain parts of the tub itself typically right around the water line. It also seems to be building up on the cover. 8 person hot tub with ozone. All I really use is a capful of chlorine shock granules after each use. When I check my chemistry, the only thing that I can never get into the "normal" or optimal zone is the Free chorine. But most others are within normal range. Thanks for the help! Jay Quote Link to comment Share on other sites More sharing options...
chem geek Posted February 12, 2016 Report Share Posted February 12, 2016 Scrape some off and put it in a ceramic dish or glass cup and add a small amount of acid to it. If it fizzes then it's calcium carbonate (i.e. scale) and one or more of your pH, Total Alkalinity (TA), or Calcium Hardness (CH) are too high. If you are using test strips, they are not generally accurate and you should get a Taylor K-2006 or TF-100 test kit. Quote Link to comment Share on other sites More sharing options...
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