Total alkalinity rise after putting on solar cover for 3 weeks?

[carpainterinaz]

Not sure if this is the right area to post, but I have a question in regards to total alkalinity rise after putting on the solar cover for 3 weeks now.
I pretty much kept my TA at 70 for the last 4 months, did weekly TA tests with my own test kit and speed stir. Last week my TA tested 90, have done 4 more tests over the last week all read 90. Is this normal after covering your pool for a bit? I'm not closing it, still warm enough to swim hopefully till the end of the month. I'm dosing daily with 10% to 8fc and keeping ph between 7.4&7.6 Iv also noticed less ph rise weekly with the cover.
I did a search but didn't find any info

 

[chem geek]

No, that's not usual since a cover should stop evaporation and refill which usually increases TA and CH from fill water. With a cover, the water chemistry should be more stable. You are seeing less pH rise with the cover which just shows most of it was due to carbon dioxide outgassing. If you are still seeing some rise, then that may be from the plaster (pebble interior).

So I don't know why you're seeing a TA rise. Make sure your dropper tip doesn't have static electricity and that the drops are fully formed for the TA test.