I just converted to a saltwater pool. Discovered my tester was faulty and my CYA is actually not 80 but 140 (years of adding stabilised chlorine).My free chlorine is a dismal 0.2 and my total chlorine is 4.2. Clearly the CYA needs drastically reducing, but with strict water restrictions in place, partially draining and refilling part of the pool is prohibited. To lower the total chlorine I was about to shock the pool with unstabilised chlorine, but will it actually lower the total chlorine with such a high CYA, or make it worse? …and does anyone have experience of lowering CYA when partial draining and refilling is not an option?
Indeed I have, to counter the effects of CYA you need to increase the free chlorine level. CYA diminishes chlorine by binding to it so you need sufficient additional chlorine to provide a sanitising free active amount. Although what I suggest may sound extraordinary it is based around correct chemistry so no need to panic.
With a CYA of 140 your normal range for chlorine is from 7-10.5 ppm and I would err on 10.5ppm. (5-7.5 % of the CYA figure)
To shock the pool you need 56ppm (40% of the CYA figure)
Whilst the oxidisation of CYA is slow the high chlorine level does begin to reduce the CYA a bit. I would continue to use Brico shed eau de javel for the cheap source of chlorine and shocking a pool is a process and not a product so holding the high level until you get better combined chlorine figures is advisable.
Thank you, that’s very helpful. Just for clarification, the high chlorine figure you quote is it total chlorine or combined chlorine- and will shocking be of any benefit right now?
The high figures are free chlorine. Obviously you cant test 56ppm so just calculating and adding is the only way then using a dilution method to get somewhere near.
You have high combined chlorine so you have an issue, it could go green anytime
I appreciate your clarification. Just an additional question. Will salt levels be an issue with so much chlorine?
No salt level will be fine, the reason for using eau de javel is to save your chlorinating cell. When chlorine breaksdown it leaves behind salt so all pools are really salt pools to a greater or lesser extent.