I don’t understand TA and CYA changes I’m getting

[Ollie0925]

Hi Everyone, thanks for help. New pool owner here. I started with half empty swamp pool in March. I refilled pool and CYA level was 80. With this website and forum I SLAMed the pool and it went great. Loving my pool which is clean and clear.

Two questions.
1) 4-6 weeks ago we had a lot of rain. I drained 4-6 inches from the pool over a few weeks. Afterwards CYA was 60. I was surprised at drop but pleased. I had to drain 2 more inches after that, and since have filled pool often with well water due to typical all day long blazing NC sunshine in the summer. Pool temps 85 degrees. In the last week I’m losing a lot of FC each day 4 or even 5 ppm but pool looks great. Today I rechecked and CYA is down to 30! How did that happen???

In case you need it. Tonight’s check FC 6 CYA 30 TA 30 pH 7.6 before new chemicals.

2) When I opened pool pH was low ( in March) and I added pH UP. TA and pH went up. TA has been consistently 70-80 and pH 7.6 ever since with no change. My nephews are heavy splashes but I was very surprised to see today’s TA suddenly low at 30 but pH exactly the same as always at 7.6. Why didn’t pH change too when TA went down.

Thoughts? I test FC everyday but confess i check other tests only every 2-3 weeks

 

[Teald024]

Hello and Welcome to TFP!!

The CYA is stable and only goes away when you drain the water or splashout. First drop could be explained with draining and typical variance reading CYA levels. Drop from 60 -> 30 is not so easily explained. Either half the water was drained and refilled or their is some larger testing variance occurring. Intense sun does degrade CYA over time, but not quickly. Higher FC loss could be explained with low CYA. Do an Overnight Chlorine Loss Test and if all looks good, then add some CYA back in.

For the TA, I again suspect some testing variance. TA drops with acid additions or adding water with lower TA. How are you chlorinating the pool? Perform the TA test again and make note of the starting water volume (25mL) and multiplying drops by the correct factor (drops x 10). You only needed 3 drops to get no more color change?

 

[Ollie0925]

Appreciate the insight. You can see where I got confused. The drop from 60 to 30 was not accompanied by water exchange except a few inches. I’ve redone the test three times and same results. My overnight chlorine loss is almost zero. The only factor is blazing all day sun. I’m chlorinating with liquid chlorine per TFP.

As for TA, I was careful to do test correctly and repeated it. It changed in only three drops and I was shocked. I can correct each of these issues but felt I was missing something. Plus after starting with crazy high CYA it seems almost incomprehensible to add stabilizer!