FC went from 7 to 0

[Jcolapin]

I used my TF-100 new two days ago. results were as follows:

TC 2.5
CC 0
PH 7.5
CH 220
CYA 75
Salt 2500
Borate 15

I added 2 gallons of bleach as per the pool calc and tested it yesterday morning and FC came up to 7. Later that night I added 5 bags of salt. I tested 24 hours later and my FC is 0.5 CC 0.5. Any ideas how I lost so much FC with a CYA of 75?

What to do next?

Thanks.

 

[Isaac-1]

Try an overnight chlorine loss test to see if you have something growing in your pool.

Pool School - Perform the Overnight FC Loss Test (OCLT)

 

[Jcolapin]

Thanks. I did o an oclt about 5 days ago and it was ok. Should I bring up the FC back to 6 first?

 

[Texas Splash]

You mentioned that you did the OCLT about 5 days ago, but you just got your TF-100 a couple days ago. With a CYA of 75 (round-up to 80) in a SWG pool, your daily FC level is 6 ppm and should never be below 4. Your FC was so low before it's very possible you have algae trying to bloom which is why Isaac-1 suggested a new OCLT. If you still find your FC crashing so much in a 24 hour period, it's probably time to do a TFP "SLAM" (link below).
Pool School - Perform the Overnight FC Loss Test (OCLT)