Why are my levels at zero when open pool?

[Arcpool13]

Just curious, we have been living at our house with our in-ground vinyl pool for three seasons now. Everytime we open, our FC and CYA are at zero. Why is that?

IS it just runoff and snow etc that is replacing the water? During winter the pool is covered with a mesh cover. Just curious, obviously never been in danger of having too high CYA, since I need to get it to minimum levels each year.
Live in Maryland. Thanks.

 

[blazer58]

IS it just runoff and snow etc that is replacing the water? During winter the pool is covered with a mesh cover. Just curious, obviously never been in danger of having too high CYA, since I need to get it to minimum levels each year

Correct, happens to most with a meh cover.
This spring was the first time I had CYA left from the fall at opening