Interesting problem, loosing CYA but nothing else

[ParB]

I test my FC several times a week. I do the full titration test every couple of weeks.
A month ago I had CYA of 50 and 4000 salt.

Today I have 30 cya and 4000 salt. I can't imagine I have a leak (I use a water alarm called flume to alert me for leaks and I have seen nothing that can explain this). Also if I loose water I should loose salt too? I have an autofiller on my pool.

I've noticed in the past few weeks that I have to increase my SWG output to get FC up more than typical. I've been blaming the sun and the hot weather but low cya is a good reason for why I can't keep FC up. The other values look stable and haven't changed over the past month eg TA and CH.

Any ideas? I'm going to add CYA tomorrow after I test again.

 

[trivetman]

Cya does degrade slowly. Its also real easy to to get a test result +-10 or more from actual depending on sunlight and your perception of the dot. Just add some cya and don’t think too hard on it