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The question is would it be better to just let it go down naturally or would it be better to use Sodium Thiosulfate? Are there any negatives associated with Sodium Thiosulfate.?
The pool is plaster and the CyA is 50 ppm. The weather is sunny and most probably the CL has now dropped to 30 ppm.
Looking forward to your replies.
Plaster pool....no harm done.
If it makes you feel any better, having 40 ppm FC in a pool with 50 ppm CYA is equivalent (at pH 7.5) to having only 3.5 ppm FC in a pool with no CYA (in terms of "active" disinfecting chlorine amounts). I think you are fine just letting the FC drop naturally as you will probably lose about half of it during each day of sunlight.
Adding sodium thiosulfate would just end up putting sulfates into your pool and I don't think is worth it. I would think that it is only used in commercial pools after shocking with chlorine when they want to re-open the pool right away.
Richard
Thank you both.
Now I will sleep better this evening.
Aloha