Accuracy of FAS-DPD at high CL levels/high CYA

[s1njin]

As prompted by a Mod, I've started a new thread regarding the above.

Using this as my backdrop: http://www.troublefreepool.com/content/215-FAS-DPD-Chlorine-Test and making special note of the last line of the page -

• The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.

I had postulated how it would be possible to pass a OCLT if your CYA was up around 70 (or higher). Shock level for that is 27.5 - so most I'm sure would use 28 or maybe even 30. At 56 -60 drops to ascertain your levels, how can one pass a OCLT with a 2 drop max deviance if there could be up to a 6 drop margin of error on the test?

I had offered it might be 'easier' for those of us with high CYA to just SLAM for a week, and if the pool is clear and the CCs are .5 or lower perhaps letting the FC drift down to 10 before doing the OCLT would yield better testing results.

So - here we go. What am I missing?

 

[duraleigh]

The OCLT was never intended to be scientifically bullet proof.

It is a darn good indicator that you have eradicated the organics in your pool.

Dropping the FC down to a range (like 10 ppm) that gives you some common sense results is a good idea.

 

[s1njin]

Thanks Dave. Would it be helpful to note something like this in the SLAM procedure?