Hello, I have been using the TFT-100 kit for a year now and have noticed some results lately that seem weird. For background, we live in Las Vegas, where it rarely rains and untreated incoming water is both very hard and very alkaline. To cope with those issues, I installed a dedicated water softener for the feed line and completely drained and refilled the pool, mostly with soft water and just enough hard water to get the calcium to the minimum acceptable level. As of March, things were nearly perfect: CH 250, TA 90, CYA 56, and Salt 3400. Lately I have been getting results every time like today: CH 375, TA 60, CYA 39, and Salt 4000. These numbers haven't just popped up suddenly, they all show a steady trend.
Fortunately today's results in PoolMath still show the water balanced and everything is normal and pool is crystal clear -- but the situation doesn't make sense to me and I don't like the trend. The CH shouldn't be going up at all. I just checked the output of the water softener and as expected, there is NO calcium in it -- I add 10 drops of R-10 and 3 drops of R-11L and the softener water comes out blue right then and there (red indicates the presence of calcium). So where could the increased CH be coming from? The only other information I can think of is that due to the highly alkaline water, the PH tends to creep upward to 8.2+ and the TA wants to rise to 100+, and thus to counteract this, I have been adding enough acid to keep the PH down to the low 7's and the TA between 60-70. Maybe pool corrosion? However, I have never gotten results from PoolMath showing corrosion of plaster (Pebble-Tec) is likely nor have I detected any noticeable corrosion. In looking at my spreadsheet of past results, however, it does seem like the more I have lowered my TA, the higher my CH has gotten.
I also don't understand Salt could be going up while the CYA is going down. When we used to live in Florida, we'd get heavy rain that would overflow the pool and that would account for lowered salt and CYA levels, but that's hardly the case here. Here we have a lot of evaporation. But you'd think that evaporation would make them both go up, not just Salt.