OK, so I added CYA in say March, then when returning from vacation around early July realized it was zero, so I did a bunch of stuff, the pool was setup pretty well.
CYA was 70-80, SWG, TA 90, CH 300-350
Now about 40 days later, I'm at:
CYA <20 maybe zero
FC 1 or less
Now in this time, the pool is 5ft deep, there's a spa, the water has been 90+ deg in the pool. There is a safety pool cover.
The SWG had problems keeping up with heat/sun/ and it was in desperate need of cleaning which I just got done last week. So the 40 days was probably FC 1 at best as it just couldn't keep up. This is SWG at 100% I'm assuming now that it's cleaned it will be different. Mind you the pool looks great, clear, blue, etc. non-chlorine shock used every 1-2 weeks.
The PH fluctuates as I assume now all SWG pools do, I try and keep it at 7.4-7.5 but it constantly climbs.
I'm wondering what if any factors would cause the CYA to disappear as it does seem strange from what I've read.