Free chlorine & Total chlorine read identical

[rtv]

I have a 30k gal in ground vinyl pool. I have been using the Lamotte Color Q regents with digital readout for testing.
Since mid Sept, about 6 weeks now, the readings for free chlorine and total chlorine have been identical.
The PH stays stable at 7.4-7.5, the alk stays between 90-105, cya stays stable in low 30's.
I keep 1 chlorine tab in the chlorinator.

Even after I shocked the pool the FC and TC stayed identical at high levels as well as when they worked their way down to lower levels.
The regents aren't old, were purchased earlier this year and stay in the house.
Can anyone explain why these two reading are staying exactly the same?

I have been testing the same way for years and almost always got a slightly different reading between them.
Could it just be the regents are bad or something else?
Or is this not abnormal?
Thanks.

 

[pabeader]

Not knowing anything about the Lamotte system, what I would say is this. If FC and TC are the same, all that means is you don't have any CC. That is considered a good thing and not to be worried about. But if you want to be extra sure, you should purchase one of the recommended kits and then you will know for sure.

 

[BuckeyeChris]

So would I be correct that, if for YEARS you've been getting measurably different CC and TC, and that you considered that to be normal or preferable?

TC=FC+CC. If you've been getting a TC more than .5 or 1ppm over your CC reading, then you've been fighting some real water chemistry issues for years also. As Bob said, zero CC is the goal. Most of us here don't even measure TC, because without knowing the underlying readings that add up to TC, it is a useless number.

 

[JoyfulNoise]

Welcome,

TFP does not recommend the use of digital pool water testers since they are prone to error and calibration problems. You can search TFP and find many, many threads of people who owned LaMotte ColorQ's and were happy for the first few months only to find that the units started to show calibration problems. The Taylor titration reagents we use here are the best-in-breed for pool water analysis and have shown themselves to be the most reliable way of measuring your own pool water. Everything else, is the "JV squad" at best...

Technically speaking, it is entirely possible for TC = FC because TC = FC + CC. So if your combined chlorine level is 0ppm, then TC = FC. However, you seem to indicate that historically that is not the norm for your pool water. Therefore I would say that your testing is now suspect and you should try to confirm that your LaMotte ColorQ is indeed reporting accurate results.