cya chart

[msachen]

Good morning experts,

Everything I've ever read ( on the side of bottles, mainly ) advises to not re-enter pool if the chlorine levels exceed 5 ppm. Yet the cya chart advises a fc level of 7.0 with a cya level of 60. What to do?

Thanks,

Mike

 

[Richard320]

How technical do you want to get? Pool Water Chemistry

The CYA binds to the chlorine molecules and buffers them. So 5 FC with no CYA would probably irritate your eyes and bleach out swimsuits in a hurry, yet 5 FC with 50 CYA is less active than most municipal water supplies that people drink and bathe in.

What to do? Follow the chart.

 

[jblizzle]

Why you should believe the random strangers on the internet

But, seriously, the pool industry does not acknowledge or understand the relationship between the CYA level and the FC level. Most of the industry still follow the EPA guidelines for drinking water when it comes to chlorine levels ... and pools are not drinking water.

The CYA buffers the "harshness" of the chlorine in the water ... in fact, following the recommended CYA/FC ratios that we post will typically make your pool MUCH less harsh than most un-stabilized public pools.

Here is a chart that shows the relative "harshness" of the active chlorine level:
https://www.troublefreepool.com/~richardfalk/pool/HOCl.htm

You can see in the table that with a 0 CYA and a FC of 5ppm ... the active level is 2.4ppm
At a CYA of 50ppm, you would need the FC to be up around 40ppm to be the same active level.

We generally say it is safe to swim when the FC is between the minimum FC and the shock level FC for your CYA as shown in the FC/CYA Chart