So as a guest, I took advice given here and went to Walmart and purchased a HTH-6 titration kit and dumped my strips. I am having recurrent issues with Algae, no big surprise given the chemistry, and my first use of the HTH kit told me pretty much what I thought about my pool water at the moment. Very low (7.0) PH, low to no chlorine levels, (although I distrust the reading due to PH being off). TA is 60. Total Hardness around 240. So here is the one that gets me, and I thought I'd ask before I just started massive dosing with stabilizer. Tested twice, I just can't get ANY reading of CA with this kit. I tested my water supply as well as a check, got nothing. I wouldn't think any of this is odd. We have never used stabilizer, get a ton of rainwater which causes dilution when the pool overflows, and since my water supply is cistern-collected rainwater typically full of sahara dust and monserrat volcanic ash (alkaline), we are forever adding acid to correct PH. EXCEPT that all summer we have been using chlorine pucks to boost chlorine levels as a supplement to my SWG, and I thought this was supposed to have a CA component, which is not showing up....

Should I believe the test and start adding CA?

Thanks, David.