Pentair IntelliChlor Salt Reading versus TF-Pro Salt kit reading

[JGrana01]

I’m still new to pool ownership and have a question.

After I purchased my house with it’s 16000 gallon pool, I upgraded to an IntelliFlo VSF pump, IntelliCenter control panel and an IntelliChlor 40 SWG.
It was early winter in Redding CA and the pool was around 60F (and dropping) so the SWG was not plugged in until this past month.
The pool is now around 80F and I added ~400 lbs of salt and we plugged in the IntelliChlor. Been working will the past 2 weeks - my FC is around 2.5-3PPM with the IntelliChlor at 40%.

I use the TF-Pro Salt kit and have been doing readings the past few months. Getting the hang of getting good measurements. After turning on the SWG I have added the salt test to the sequence.
The one thing that I have noticed the past week is the difference between what the TF-Pro kits says my salt level is and what the IntelliChlor app shows me.
When I first added the salt (IntelliChlor not yet plugged in) I hit my target pretty well. TF-Pro showed me around 3400 ppm (maybe 3500 if extrapolate the 200 ppm drops).
We plugged in the SWG, set it to 50% and let it run a few days. FC was good, I was (pre SWG) around 1-2 ppm, after a few days of SWG up to 3 ppm.
The Pentai app showed me IntelliChlor said I was at 3150 ppm salt. TF-Pro said I was still at 3400 ppm.
Today, IntelliChlor says I am at 3000 ppm, TF-Pro says I am closer to 3300 ppm).
Am I not doing the TF-Pro test correctly or is the Pentair IntelliChlor typically off (in this case seems around 250-300 ppm)?

BTW, tfp has been a great resource - especially for a new pool owner! Many thanks!

 

[Texas Splash]

It is very common for the SWG and actual salt drop testing to not match. Sometimes I have a significant difference of several hundred ppm. So there are a few things to consider:
- Never expect them both to match, it's not realistic.
- In most cases, as long as the SWG is not throwing any errors, it's producing FC and that's good.
- Knowing your actual salt level via drop testing is still good because it gives you an accurate perspective if the cell might be showing signs of faulty readings.

Try not to let it get to you too badly. If you're producing FC, chances are everything is fine.

On a side note, your FC has dropped low a couple times and that's neve a good thing for the water or SWG. Keep some liquid chlorine handy to increase the FC right away when it falls like that. Always go back to the FC/CYA Levels to see what your FC level should be. Hope that helps.

 

[Jimrahbe]

01,

You should never, ever trust what the cell reports as the salt level unless you have a way to verify it. An IC40's reading is +/- 500 ppm, the test kit is 200ppm.

Always believe the test kit. Saying that, you have to keep the cell happy, so if the cell thinks the salt is low it won't work no matter the actual salt level. As long as you can keep your "Actual" salt level below 4000 and make the cell happy you are good. If you have to go over 4K, then you most likely will need to replace the flow switch which has an temper sensor that can go bad.

Thanks,

Jim R.

 

[JoyfulNoise]

IC-40 salinity readout is basically an electrical conductivity (EC) measurement with a calibration factor for salt. It’s an inferential, or proxy, measurement.

The K-1766 salt test is a chemistry test - it actually measures the number of chloride ions in solution and it has no positive interference from anything dissolved in the water (unless your pool happens to have cyanide in it …). So it is a DIRECT test for chloride.

Which do you suppose is the more accurate test? (Rhetorical question, of course).

One thing to understand about the IC units is that they use a thermistor built into the flow switch to measure temperature. The electronics uses the temperature value to adjust the reported salinity value because conductivity is affected by water temperature. It’s not a very good setup because the reported conductivity drifts a little with temperature. If the thermistor goes bad on the flow switch, the reported salinity will vary A LOT with temperature. And, when that happens, the cell will sometimes stop generating if it thinks the salinity is too high or too low. The flow switches and their thermistors go bad a lot. So don’t be surprised if that’s something you might have to fix in the future. Thankfully it’s a very easy DIY swap out of parts. But wonky temperature/salinity readings is a sure sign the thermistor is faulty.

 

[JGrana01]

Thanks for all the infomation and advice! I’m OOT for a few days and will check the salt level via TF when I get back.
The system is happy right now and making chlorine well.