Salt test level doesn't match the system read out

[SuzfromTexas]

I've been testing the salt level in the pool since it was switched over the end of August (a month after the pool was filled). The Taylor salt test was always neck and neck with the read out on the PDA for the salt level.

Yesterday and today the salt test readings have been 2400 and 2600. I ran the test twice yesterday and twice today. Both days the reading on the PDA has been 3100.

Water temp is 66 degrees.

I found this quote from a post by JasonLion when I was trying to find the answer. "Pool store test results are legendary for being wildly wrong sometimes. As long as the SWG appears to be working, trust it's salt readout over the pool store. The only times when a SWG salt readout is normally wrong is when the water is cold or the cell is about to fail. When the cell is failing the salt level will read lower than actual. It is more or less unheard of for the salt level to be wrong high, and common for pool stores to be way off, so I wouldn't worry about it."

I just had pool school on Friday, and the guy told me to add salt when the level was down around 2800. So the test results have me concerned. I had just switched from testing every other week (weekly the first few weeks to get used to the test) to once a month. I think I shouldn't have done that.

So, is there something wrong with my test? The code on the bottles is April 2016. Or does it not work as well in cooler water temps? (66 today)

If anything, I'm struggling to keep the FC lower within range. It was 9 yesterday and again today. Yesterday I reduced the pump run times. Maybe that takes a day or two to bring down the FC.

But if the FC is still in the pool, doesn't that mean the salt cell is 'happy'?

And the water looks great.

Thanks. Just when I think I'm sailing smoothly along, I get this little blip....

Suz.

 

[duraleigh]

Disregard that variance. Many folks report a variance of even more. As long as your SWG is producing chlorine, let it alone.

 

[SuzfromTexas]

Thanks Dave! That's great to hear!
Suz.

 

[eqbob]

My salt cell goes astray from the true reading by a Taylor salt test the colder the water gets. By the time it gets low 60s water temp I don't even pay attention to what salt cell says because it is too far away from its calibration temperature. My salt cell is pentair and that's my only experience so the caveat is that other brands may act differently. Low 60s to high 50s water is time to start using bleach.

 

[JoyfulNoise]

Suz,

Many SWGs are not temperature compensated which means that, as the water temperature changes, the output "salinity" reading of the electronics will vary. I put "salinity" in scare-quotes for a reason - no SWG actually measures salt level or salinity, they measure the conductivity of the water by passing a small electrical current through a probe and measuring resistance. Since solution conductivity is temperature dependent, so too is the output reading.

So what should you do? Don't measure your salt level more than once or twice per month (or only after a big water exchange, like heavy rains). Your K-1766 is the most exact measurement (+/-200ppm). As long as your K-1766 shows you to be in range and your SWG is happy (green lights), then don't worry about your salt level. One thing to remember, despite what the pool "experts" say, is that SWGs are very forgiving and can easily and efficiently produce chlorine over a very wide salinity range. So it would take A LOT of water loss to make your cell stop producing chlorine efficiently.

Hope that helps,
Matt


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[lefty51]

Hi Suz, JoyfulNoise said it exactly.

I think you'll find that over time you can test the salt level once a month with the K-1766 and use the SWG readout as a quick reference that all is ok.

Unless there is significant water change, your salt level should stay pretty constant. During "normal" water temp, just glance at the SWG reading occasionally and if it shows something dramatic or low salt light comes, then dig out the Taylor and verify.

As Matt said these things are very forgiving

 

[eqbob]

And in reality, you don't even really need it once a month during the warmer times of the year, because it won't be reading low, or when the water temp is low 50s because it isn't producing anything anyways. I find fall to early winter and early spring is when I have to test and ensure that the cell reads happy and is somewhat correlated with the actual, via the Taylor test. Those are also the times that are more prone to the monsoon rains in my part of Texas.