IC40 SWG - What could be causing the salt level to keep dropping?

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peterl1365

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LifeTime Supporter
Mar 28, 2007
279
Murrieta, CA
Pool Size
13000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I've got an IC-40 cell that I installed in April 2013. After some salt-level issues last year, it worked generally ok through last summer and early fall.

This year, I fired up the pool around the 2nd week of March. Salt level reading was around 2600 ppm, slightly lower than the ~3100 ppm that I had at the end of last season. So I added a couple of 40lb bags. That brought my levels up to around 3000 ppm again.

About 3 weeks ago, I noticed the cell light was red again and the CL levels were near zero. Salt reading was back down to 2600ppm. So I added another bag, and the reading jumped back up to the 3000 range.

This morning, I tested the water and the CL levels were low again. Sure enough, the cell light is red. Salt reading was now down to 1950ppm. I inspected the cell plates and confirmed that there was no visible scaling. There was some green matter (grass blades) partially impeding flow, so I cleaned that out. Remounted the cell after the initial test period, the salt level is reading 2250ppm.

What could possible be causing this? I'm not sure if it's the IC40 or if there is something else going on.
 
FWIW, I have ruled out a leak. I've had the autofill turned off for the last 4 weeks following a rare heavy rain here in So. California. In that time, the water level has dropped by less than an inch.

I don't mind adding more salt, but I'm afraid that the "true" salt levels are approaching dangerously high levels. I had a similar situation last year following the initial installation. Started out at around 3400 ppm (measured at Leslie's Pool), then all of a sudden, the reading was ~1700ppm. I had the water tested at a couple of different pool stores, and they all measured at around 1900-2000ppm.

After scratching my head for a week, I relented and added about 4-5 more bags. This brought my readings to ~2900 ppm, but I've long suspected that the levels were inaccurate. At that point, I had around 13 bags of salt added to water that already had ~750ppm from a few years earlier when I stopped using a SWG for a while.

Now, I've got around 15-16 bags of salt in the ~13,000 gallon pool. There's been no significant drainage or splashout in the 13 months since I've put in the cell. By my math, I should be up above 4000 ppm. As a point of reference, when we first got the pool in 2007 and filled it with fresh water straight from the garden hose, I used only 10 bags of salt to bring it up to ~3500 ppm.
 
If you truly are concerned about high salt readings, I'd stop getting salinity tests done at a pool store and get a Taylor k-1766 and get the most accurate tests possible. When I first looked into getting a swg early this spring, one of the online stores I considered in the purchase process, told me I'd need to throw a bag in the pool every couple of months. Since you've given us no real indication over what period of time you've put that 15-16 bags of salt in, it's really hard to determine if your usage is unreasonable or not. Also, if you're cell is telling you it's happy with your salt level, I.e. not shutting down for low or high salt, just go with what you have. After all is said and done, it's what the cell thinks it is that's important.
 
what is the water temperature ?

The cell reads 3400 ppm at 77 degrees F if the salt level is at 3400 ppm...and loses 200 ppm for each 5 degrees F....example ...if temperature is 68 degrees F then 77 - 68 = 9 degrees and you subtract 200 ppm for each 5 degrees below 77 degrees.
 
timerguy said:
If you truly are concerned about high salt readings, I'd stop getting salinity tests done at a pool store and get a Taylor k-1766 and get the most accurate tests possible. When I first looked into getting a swg early this spring, one of the online stores I considered in the purchase process, told me I'd need to throw a bag in the pool every couple of months. Since you've given us no real indication over what period of time you've put that 15-16 bags of salt in, it's really hard to determine if your usage is unreasonable or not. Also, if you're cell is telling you it's happy with your salt level, I.e. not shutting down for low or high salt, just go with what you have. After all is said and done, it's what the cell thinks it is that's important.
Click to expand...

I should clarify: The salt readings are from the cell, and they have been verified, from time to time, within about 10-15% by the pool store. My salt cell is currently non-operational because it is reading below Pentair's threshold level of 2600ppm. I understand that pool-store readings can be inaccurate, but I'm not relying on them.

The 15-16 bags of salt are what I have added since April of 2013. As I understand it, there should be very little loss of salt unless I drain water from the pool. I live in a very arid environment, with a lot of evaporation, but that should not significantly affect the overall amount of salt in the pool. I don't really see the need to continually add salt unless there is an extreme amount of splashout. I have a cartridge filter, so I don't do any backwashing. Adding a bag every couple of months doesn't seem correct, unless you have a very large pool.
 
susa said:
what is the water temperature ?

The cell reads 3400 ppm at 77 degrees F if the salt level is at 3400 ppm...and loses 200 ppm for each 5 degrees F....example ...if temperature is 68 degrees F then 77 - 68 = 9 degrees and you subtract 200 ppm for each 5 degrees below 77 degrees.
Click to expand...

The water temp in March was about 62-65 °F. Currently, it is about 70-74 °F. The temperature varies slightly as the sun heats it up during the day and then it cools off at night.

I understand what you're saying about the temperature variation, but what I'm seeing is the exact opposite of what I would expect. The salt cell readings have dropped, significantly, as the water has warmed up.

I will try taking a water sample into a pool store to see if their results correspond with the salt cell. FWIW, I have some salt test strips left over from last spring. As far as I can tell, they are reading between 2000 and 2500 ppm. Obviously, I don't place great trust in those because of their age and the general problem with using test strips. However, they do seem to somewhat validate the salt cell readings.

So, if the pool store verifies that I've got salt in the 2300ppm range, is there any possible explanation for the drastic losses? Keep in mind that as little as two weeks ago, the salt cell indicated 3100 ppm, and I thought I was all set for the summer.
 

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You should do a visual inspection of the SWG cell and see if there is any white chalky stuff on the cell plates. If so, you need to clean the cell (dilute acid bath) and adjust your water chemistry to prevent further scaling.
 
Butterfly said:
Well, I know you said the auto-fill is off, but maybe you should double-check it.
Click to expand...

I can double-check it, but I'm pretty certain. I've shut it off at the equipment pad, and it's a quarter-turn butterfly valve, so it's pretty unlikely that it would be leaking water. Even if it were on, the current water level is about 1/2 inch higher than where the auto-fill normally turns ON. That is due to a couple of late winter storms over the last two months that raised the water level up by an inch or two.

I can also speculate that the rains might have diluted the salt levels, but not by the drastic levels that I have seen. Also, the readings were ~3000ppm last weekend, and we haven't had any significant rain in the last 2-3 weeks.

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I may do that. The primary reason that I haven't is that I'm color blind, so performing the drip-based tests is very difficult for me. I use an Aqua-Chek Tru-Test meter for my daily testing. I know that it's not that accurate, but it at least lets me maintain my CL and pH within an acceptable range. I pay more attention to the moving average than I do to any particular reading.

Is there a standalone drop-based salt test that doesn't rely on color vision?

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JasonLion said:
You should do a visual inspection of the SWG cell and see if there is any white chalky stuff on the cell plates. If so, you need to clean the cell (dilute acid bath) and adjust your water chemistry to prevent further scaling.
Click to expand...

I've already inspected the cell, and there is no buildup that I can see. I may do a cleaning anyway, since there might be a slight film forming on the plates that isn't visible to the naked eye.

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737mech said:
I would invest in a test kit that has been suggested http://www.taylortechnologies.com/products_kitinfo.asp?&MarketID=-1&KitID=2176
Google it to find the best deal. Testing the salt level yourself is the way to go. From what you have said it doesn't seem reasonable to be adding that much salt if the pool water isn't being pumped out.
Click to expand...

I may have to do that. The primary reason that I haven't is that I'm color blind, so the drop-based tests are very difficult for me to deal with. I use an Aqua-Chek Tru Test meter for everyday testing. I know it's not very accurate, but it helps me keep the pH and CL within a generally acceptable range. I'm more interested in the moving average than in any particular reading.

Is there a drop-based test for salt that doesn't rely on color vision?
 
By the way, thanks again to everyone that is trying to help me out on this. I'm really stumped on this, and I appreciate any ideas that you may have.

FWIW, here's some background info on the issues I had last year. It all started about a week after I added borates to my pool for the first time. I can't say that the two are related, though. But it might be a possibility.

http://www.troublefreepool.com/threads/55077-Pentair-IC40-cell-no-longer-working

Another long-shot possibility: Over the 7 years we've had this pool, I've always had to fight rising calcium hardness levels. I think it was a combination of new plaster and relatively hard fill water. Generally, I would counteract this by making sure my pH was under 7.6 and do a partial drain-and-fill when the CH levels got to the 800+ levels. The last 12 months or so, however, the CH readings have been consistently under 400ppm. I think the last drain-and-fill I did was December 2011.

Is it somehow possible that the NaCl ions are somehow reacting with the borates and the calcium to somehow bind up the salt AND the calcium? The chemistry is far over my head, but maybe someone else might know.
 
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