Salt Levels: Depends on Measuring Device

[peacefulkancer]

It is already starting to get hot here in Phoenix, AZ, so it was time to start getting things in order. I noticed that my IC40 was flashing for the salt level (high @7000). I took the IC40 off and cleaned it as it needed it. Hooked it back up and then it was reading 1980ppm. (NOTE: pool temp is 66ºF)

Did a NaCl check with my AquaChek 561140A Salt Water Swimming Pool Test Strips that I got last year and it read 5200ppm.

I know that the strips go bad with moisture but we are talking about Phoenix here... we get like 5 days of rain. The strips were also well out of the rain and in storage. I figured I'd switch to reagents and ordered the TAYLOR TECHNOLOGIES INC K-1766 DROP TEST and it game me 2000ppm. So it seems the IC40 was reading correctly. So the AquaCheck strips are out as they are probably bad. Maybe we had extra moisture this year during our Monsoon season?

So I have two questions:

1. What is the NaCl skew based on water temperature? I read elsewhere that for every 5ºF off of 77ºF it changes the ppm 200ppm.
2. How long does the K-1766 reagents last?

 

[ajw22]

So did you add salt to get above 3000ppm and get your IC40 running?

@JoyfulNoise may know the answers to your chemistry questions.

 

[JoyfulNoise]

The IC40 has a thermistor in the flow switch that is used to read water temp. If that goes bad ( and they frequently do), you will get spurious salt levels. The cell is supposed to compensate for temperature so you really should only see minimal drift with water temperature. When I replaced my flow switch last year, the salinity readout was stable with temperature all the way down to the cold water cutoff temperature.

The K-1766 reagents, when kept indoors and in a cool dark space, will last years. The silver nitrate reagent will go bad if it’s left out in high temperatures, humidity or with high sun exposure. My kit has lasted for years now and it’s still dead-on accurate.

 

[peacefulkancer]

So did you add salt to get above 3000ppm and get your IC40 running?

@JoyfulNoise may know the answers to your chemistry questions.

I added one 40# bag to see if the salt level went up or not according to the K1766. It did. So I just added another bag and am watching it accordingly. I think after it is said and done I will need 1-2 bags other than the two I added this week. Currently at 2500ppm. According to IC40 manual need it at 2800-4500ppm for the IC40 to be happy.

I feel kind of weird about this as at my last house I never had to add salt, much less multiple bags. But then again, last year was my first season at this house/pool and maybe I opened the pool last year with not enough salt (I inherited a non-SWG and converted to SWG).

The IC40 has a thermistor in the flow switch that is used to read water temp. If that goes bad ( and they frequently do), you will get spurious salt levels. The cell is supposed to compensate for temperature so you really should only see minimal drift with water temperature. When I replaced my flow switch last year, the salinity readout was stable with temperature all the way down to the cold water cutoff temperature.

The K-1766 reagents, when kept indoors and in a cool dark space, will last years. The silver nitrate reagent will go bad if it’s left out in high temperatures, humidity or with high sun exposure. My kit has lasted for years now and it’s still dead-on accurate.

My IC40 reads +/- 100ppm from the K1766 level so I don't think the temperature sensor is bad nor is the salt level the IC40 is reading. Not that this discounts the idea, but my IC40 is not even a year old yet so I hope it isn't bad!

 

[ajw22]

Keep adding salt, up to 4000 ppm as measured by your Taylor test kit if necessary, and see when your SWG turns on and is happy. What your Taylor test tells you and what the SWG measures can differ by 500ppm or more. Find the salt level that makes the SWG happy.

 

[peacefulkancer]

Keep adding salt, up to 4000 ppm as measured by your Taylor test kit if necessary, and see when your SWG turns on and is happy. What your Taylor test tells you and what the SWG measures can differ by 500ppm or more. Find the salt level that makes the SWG happy.

I'm slowly adding - letting it mix in plenty before adding the next bag. Again, it just seems kind of bizzare that it is/was that low.

Just for sanity's sake, lets just say it was at 3000ppm last summer. How much loss would be expected over a winter in Phoenix?

 

[JoyfulNoise]

I'm slowly adding - letting it mix in plenty before adding the next bag. Again, it just seems kind of bizzare that it is/was that low.

Just for sanity's sake, lets just say it was at 3000ppm last summer. How much loss would be expected over a winter in Phoenix?

None.

You get over 95” of water evaporation per year, that’s pretty much an entire pool volume. Your fill water will have, at a minimum, 50-80ppm chloride concentration. I once, early on, over-salted my pool up to 4100ppm. The level never dropped except when I would pump out large quantities of pool water.

 

[JoyfulNoise]

If you see your salt levels measurably decrease with time, then you should do a bucket test and check for leaks. Calcium hardness is another level that increases with time unless you have a water softener supplying your fill line. If you see CH decrease over time and you cannot correlate it to water exchange, then that’s another indicator of a possible leak.

 

[peacefulkancer]

None.

You get over 95” of water evaporation per year, that’s pretty much an entire pool volume. Your fill water will have, at a minimum, 50-80ppm chloride concentration. I once, early on, over-salted my pool up to 4100ppm. The level never dropped except when I would pump out large quantities of pool water.

If you see your salt levels measurably decrease with time, then you should do a bucket test and check for leaks. Calcium hardness is another level that increases with time unless you have a water softener supplying your fill line. If you see CH decrease over time and you cannot correlate it to water exchange, then that’s another indicator of a possible leak.

That is how the pool at my old house was - the level never dropped.

I'm certainly hoping that there is no leak. Last year when I switched over to SWG I calculated how much salt I needed and bought the exact amount of pounds that I needed (I cant remember the target value, unfortunately). I didn't put all the bags in - I still had two left over. However, the SWG was happy. I tested with the strips and all seemed well. So I can see being short 2 bags since that was 2 bags I didn't put in off my original calculation. But as of right now it seems like I am off 4 bags.

I currently have 3 bags added this season and I'm now at 2850ppm (just added it a few hours ago) on the IC40 readout so I'm going to assume that the K1766 is just a touch higher. I'll probably add the fourth bag to bring it up just a little more.

Maybe my original calculation was wrong or I targeted incorrectly and I was low last season too. Salt isn't something I tested throughout the season.

 

[JoyfulNoise]

When you add the salt, it needs to be brushed around until it dissolves and then you shouldn’t bother measuring salt for at least 24-36 hours later. The locally created brine water has a higher specific density than the surrounding pool water and, for all intents and purposes, the bulk pool water is very stagnant. So without mechanical agitation, there can be pockets of high and low salinity. Throwing kids in the pool to help mix the salt helps a lot. If you don’t have access to children, a robotic pool cleaner is a good option. Pump driven cleaners aren’t that good at it but it’s better than nothing.

 

[peacefulkancer]

When you add the salt, it needs to be brushed around until it dissolves and then you shouldn’t bother measuring salt for at least 24-36 hours later. The locally created brine water has a higher specific density than the surrounding pool water and, for all intents and purposes, the bulk pool water is very stagnant. So without mechanical agitation, there can be pockets of high and low salinity. Throwing kids in the pool to help mix the salt helps a lot. If you don’t have access to children, a robotic pool cleaner is a good option. Pump driven cleaners aren’t that good at it but it’s better than nothing.

Agreed. I have brushed it in but I'm sure what you say is correct - a lot of water is stagnant and needs to continue to mix. I'll have to toss in the Dolphin and see how much it changes. Right now the IC40 reads 3000ppm. Yesterday it read 2950ppm.

NOTE: I do have one kid. But she is one so she's not going to jump in and mix it up. And I'm an absolute wuss in that I like my water like bath water.