Walmark HCH 6 way test says din't go above 4ppm FC

[number419]

Quick question:

For the past month I've been adhering to the pool calculator and CYA charts for all my chemical balancing...and have been using the Taylor K2006 test kit for testing.
With a CYA of about 60, the chart tells me I should be around 7ppm FC.

I just looked at the Walmart HTH brochure (which I bought a long time ago), and it says going above 4ppm FC can cause bodily injury and that you are using more FC than needed.

Can someone explain why the test kit brochure says not to go above 4ppm FC, and the CYA chart says to go nearly double that amount?

Thanks!

 

[Stuamurr]

Cyanuric Acid (Stabilizer) slows down the ability of FC to do it's job, with CYA in your water some of the FC will be 'bound up' by the CYA so the FC level needs to be raised higher than this so a FC residual re-acts to ammonia in your water more readily. A lot of people in the pool water chemistry industry do not acknowledge the CYA/FC relationship, citing that the FC will still do it's job - which it will only considerably more slowly.

"above 4ppm FC can cause bodily injury" is a ridiculous claim, it is safe with CYA at 60ppm upto 23.9ppm FC to swim in "more than needed" is technically correct, but what is needed and what is effective are two different things.

Regards
Stuart