white stains on the bottom

[pplepew]

I found white stains on the bottom of my pool. Some of them have a sort of a buble on top (like water infiltrations underneath the liner)....
Where are these sopts coming from and what to do ? The pool have been covered since the begining of fall and the water is perfectly clean. I did not add any excess of chlorine either .........
Anybody could help ??

Thanks in advance

[mr_clean]

I found white stains on the bottom of my pool. Some of them have a sort of a buble on top (like water infiltrations underneath the liner)....
Where are these sopts coming from and what to do ? The pool have been covered since the begining of fall and the water is perfectly clean. I did not add any excess of chlorine either .........
Anybody could help ??

Have you done full chemical check?
FC-free chlorine
TC-total chlorine
CC-combined chlorine
PH-reading
TA-reading
CH-hardness
CYA-conditioner
this will help to start

Do you use chlorine tabs? if any have fell onto liner they can bleech it.
Sometimes ground shifts and rocks rise.
could be bad chemical balance.