I have a small 375 gallon spa in great condition (2 years old). I have a cover and keep the spa at 98 unless we are in it and then it goes to 101. I use Taylor K-2006 test kit.
A fresh fill yields the following measures before any adjustment: hardness right around 200-210; High pH greater than I can measure with kit and TA a bit greater than 200. I leave hardness alone, and slowly bring down TA with acid: 1/2 recommended and circulate; 1/2 recommended and circulate; et at until I get pH down close to 7.0, then turn on everything and circulate on high. pH comes up as it should, but TA is usually low, 60-80. On this fill, I put in first measure of dichlor to get to 6ppm and have not used the spa because it is still rather warm here, but want to be ready when evenings begin cooling down.
3-4 days after the adjustments, the chlorine was down to 1 or 2 so I checked pH. It was quite red above 8. I added acid the same way, got the pH down near 7 again, aerated and then added second measure of dichlor, but did not check TA.
We still have not used tub yet on this fill, but checked chlorine earlier this evening and in was down to 1. So I checked pH also is pH was back up above 8 again, checked TA and it is down to 40-50-- probably was down from last addition of acid. I figure if I add acid again to get pH back down even to 7.6 it will push TA down even more. I haven't added dichlor yet this evening.
Why is pH climbing like this, and how low can I let TA go. This happens every time I fill, and it seems that the only way to keep pH in range is to run with a really low TA value. Saturation index in .48 right now.
Why can't I get my TA up in range? We haven't even been using the tub yet, and I keep it covered all the time. I would appreciate input and advice.