I drained my pool down to 6" above shallow end to try and dilute iron in my pool (didn't want to add sequestrant all summer). Replaced the water and turned it over 24 hours, pump on the whole time, pulling from skimmer and drain.
Started to rebalance water to get ready for SWG that I just installed. First thing I did was check chlorine and dump 3 of the 1/2 size bleaches from aldi in the pool just to kill anything if it was trying to start (took a while for hose to refill).
CYA 0 (more on this)
My CYA had been low all winter, nearly 0. Pool was left open as I'm in the south. Added bleach as needed, usually every 2 to 3 days. Had some water get behind the liner once, I believe from overflowing when I was out of town (I think wife didn't notice until it was too late).
First thing I did was start to get CYA back up. Since I am going salt, I was going to start by getting close to 60. Per calculator, I would need 15lbs of granular CYA. I checked levels with TF100 (overflowed the tube and could still see dot) as well as aquacheck strips. 18" dip from pool after turning new water for 24 hours.
Instead of 15, I only added 12 to see where it would be. Slowly added to skimmer last night. I also added 10 bags of salt (all I could get in car - I need 11 more).
Just out of curiosity, i went to check it this morning and it was somewhere around 90!!! I checked both sides, hoping it might be higher on the return side. NOPE. STILL 90.
I immediately went and backwashed hoping to get whatever was left in the filter out of there and hopefully not have to drain it again. I probably washed out a bunch of salt as well, but oh well.
My question is, WHAT GIVES?!?
I thought I was being conservative by only adding 12lbs!
Does the CYA levels spike or something for a little while?
I don't really understand how it could happen.
PS - I forgot to mention that the PH went down to 6.8. I recall reading that the CYA test is not as accurate unless above 7? Could this and/or the cold water affect the readings??