How much free chlorine is safe?

[rdelisa]

I just replaced my chlorine generator cell this Spring. It is now working more
efficiently than I predicted. I left it on the lowest, forgot to turn it off overnight and my FC is 12ppm. This is shock level. Turned it off, but it’s a cool day and not likely to get much lower very soon. CYA is between 60 and 70. I am using the Taylor k2600 for testing. Was hoping to swim today for my daily exercise. Is it safe with such a high FC level?

 

[mknauss]

At 70 ppm CYA, your SLAM level FC is 28 ppm. As long as the FC is above 4 ppm and at or below 28 ppm, you are good to go.

 

[scchan1w]

At 70 ppm CYA, your SLAM level FC is 28 ppm. As long as the FC is above 4 ppm and at or below 28 ppm, you are good to go.

I'm curious why the recommended target FC is so close to the minimum level then? Why not have a larger offset and set the target at say 15 ppm to give headroom?

 

[mknauss]

Target is based on normal FC loss per day of 2-4 ppm. So if you are within target (high end during the peak of summer), your FC will not drop below minimum.

As you raise your FC, there is additional loss to UV over what you will see at the target range. Economy is part of TFPC.

 

[rdelisa]

Thanks!
This is interesting in that the advice is so different than what you will hear from your typical pool guy. Would you recommend a target FC of around 7PPM or approximately 10% of CYA?

 

[mknauss]

Would you recommend a target FC of around 7PPM or approximately 10% of CYA?

Yes. With a SWCG that is great spot to keep the FC level.