Autopilot salt reading versus strip salt reading

[beezar]

So I got my Autopilot Digital SWG installed and added 240 lbs of salt to my pool of 18K (estimate by one pool guy, another guy estimated at 22.5K).

The Autopilot estimated salt level prior to addition of salt to be around 1200ppm, while the Accucheck salt strip measured it at 570.

After salt addition, Autopilot said 3600 ppm while salt strip 2570. (Ideal salt range for Autopilot is 2500-3500 with 3000 ideal).

So what should I believe? Should I add more salt per the salt strip or do I have too much per the Autopilot?

 

[mx702]

I certainly wouldn't add anymore. Ultimately, it's your SWG that needs to be satisfied in terms of salinity for proper operation. I encountered the same discrepancy between the strips and my SWG with with my new pool startup. I would trust your SWG.

 

[Voodoo_Pool]

Don't add any more salt for now. Make sure all the salt is completely mixed. Since I am posting at night, I will guess that by the time you read this it will have been a few hours. Run your pump a couple of hours and re-check the salt level. Salt is tricky to measure, but strips are best. As stated you still need to satisfy the SWG. So I just corrected myself. I'll be curious if you get the same readings 24 hours later. Enjoy!

 

[splash]

The Autopilot salt sensor may need to be re-calibrated. I would trust the salt strips and re-calibrate the Autopilot to the salt strips

 

[duraleigh]

I do not have an SWG nor any salt in my pool so I cannot test. However, the consensus on the forum is that the Aqua chek strips either report on the money or sometimes a little high.

I don't remember a report of them testing lower. I would leave the salt alone and see if the SWG will make chlorine.

 

[splash]

BTW, you can re-calibrate your Autopilot salt sensor by choosing the Installer menu (press select for 13 seconds). Within the Installer menu you'll see an option to re-calibrate the salt reading. Just use the up or down arrow keys to match your salt test strips. The advantage with salt test strips is that they don't need calibration. All electronic salt sensing devices need to re-calibrated by testing in a certified salt solution of 3000 PPM.

 

[JasonLion]

The AutoPilot can be wrong, but it is more likely that the salt test strips are wrong. I wouldn't calibrate the AutoPilot to the strips without confirmation from another kind of test. You should also keep in mind that all of these salt tests are +-400, so some variation between different tests is expected (though not by quite that much).

 

[beezar]

The AutoPilot can be wrong, but it is more likely that the salt test strips are wrong. I wouldn't calibrate the AutoPilot to the strips without confirmation from another kind of test. You should also keep in mind that all of these salt tests are +-400, so some variation between different tests is expected (though not by quite that much).

Ok, probably the best thing is to use another confirmatory test as you say. Now, what other tests are there? I suppose the pool store can give me a level, but after being on this forum a few months, it seems like pool store tests are often wrong.

 

[splash]

You need to obtain a certified test solution. That's the only way to prove that an electronic meter or even salt strips are accurate. For example, if a meter reads 3200 for a certified solution that's 3000 PPM then just re-calibrate the meter or deduct 200 PPM when testing the pool water, then check your AutoPilot and re-calibrate that if necessary.

 

[Poolsean]

There's no high salt limit so there's no problem if you happen to overdose the salt level.

From the salt amount added and ppm increase indicated, one can calculate the pool volume. In your case, using the AutoPilot salt readings, you've got 12,000 gallons. Using the salt strip readings, you've got 14,000 gallons. Make sure you adjust the Pool Pilot "SET POOL VOLUME" to match the gallons. If you adjust it to 18,000 gallons or 22,000 gallons, then the unit will display to add more salt than you should, if in fact your pool gallons is really less the guesses you got.

Now, regarding the salt level, the Pool Pilot is fairly accurate from the start. Make sure you've allowed enough time for the water to circulate and distribute the salt evenly throughout the pool. At least one day of circulation.

As Jason said, if you're pool salinity is plus or minus 400 ppm from the actual salt level, you're within range. If you're too low in salt, you will see a higher voltage than is normal. This would depend on the cell model you have.
SC-36 / RC35/22: 16 - 19 volts
SC-48 / RC42: 23 - 28 volts
SC-60 / RC52: 21 - 26 volts

 

[beezar]

Just thought I'd give an update:

Tested a 0.45% sodium chloride solution (used as intravenous fluid, so accuracy is pretty high -- 4500ppm salt) as well as my pool water.

Accucheck test strips - solution measured as 3890 ppm, pool water as 2570
Pool store #1 - solution measured as 4200ppm, pool water as 3200ppm
Pool store #2 - solution measured as 4100ppm, pool water as 3000ppm
Autopilot digital measured salt in the pool as 3600ppm.

So if you assume the 0.45% solution is very accurate and not far off of 4500ppm, it seems pool store 1 and 2 with correct calibration would measure pool water as around 3500ppm and 3400ppm respectively. Thus it seems like the Autopilot is the closest measuring the pool water at 3600ppm right out of the gate. Plus it doesn't give me much faith in test strip accuracy, though I realize it's +/- 400ppm.

The only thing that's bugging me is that my SC48/RC42 cell is running at 29 volts when set at 50%, which is higher than the range that Poolsean says possibly indicating too low of a salt level...

Thanks for everyone's tips!

 

[DigitallyChallenged]

Brilliant idea using IV fluids. I resisted getting a digital salt meter because of the reference solutions. This is a game change for me.

 

[accidental chemist]

I think you need to confirm the size of your pool. If I remember correctly, you have to tell the Autopilot the pool volume. If you you lie to it, it will be confused.

 

[JasonLion]

The pool size setting only affects the amount of salt it tells you to add when you need to add salt. It won't affect the salt reading.

 

[Poolsean]

beezar, how cold is your water? If it's below 65 degrees still, it may be affecting the voltage. What's it showing for amperage? Have you checked the cell for any calcium scale?

 

[beezar]

beezar, how cold is your water? If it's below 65 degrees still, it may be affecting the voltage. What's it showing for amperage? Have you checked the cell for any calcium scale?

My water temp is 76 deg, autopilot says 28V, 6.3A, power level is 2 with purifier at 50%. I didn't check for calcium scale, but the Autopilot was installed just 2 weeks ago, and my CSI is negative, so I doubt it's calcium scale. I have a SC-48/RC-42. Now you've got me worried.... what else could it be?

Also, don't know if this is normal, but the display doesn't go to a walking dot screen saver like the manual says. It just flashes off then on the display reading every 2-3 secs or so.