Squeeze last bit of life out of cell?

[Saturn94]

Salt strips measure salinity through capillary action as the surface tension of salt water changes with salinity. Their biggest problem is that they are not terribly precise (error can be as high as +/-400ppm) and they are subject to spoiling if exposed to humid air.

Thanks for the info.

I’ve used the AquaChek salt strips for many, many years and they most always test within 200ppm of what my SWCG reports (with a good cell of course). It wasn’t until last year when I ran out of salt strips that I got the K1766 instead, of course not knowing about the potential interference with the metal sequestrant I use. I realize the SWCG and strips are not the most accurate, but they worked well to track the health of the salt cell, which is the goal of all this testing.

Now that I know there is an issue with the sequestrant interfering with the K1766, I’ll likely just go back to using the salt strips. Also, if I do suspect the cell is failing, I’ll get it tested before buying a new one, lol.

 

[JamesW]

I am the one who suggested the 75% mark as the point to consider replacing the Aquarite cell.

In my opinion, it's a good guideline.

The cell generally drops off pretty quickly once it goes below 75%.

However, I never said that anyone absolutely had to replace the cell at 75%.

 

[JamesW]

I just changed the recommendation from the first quote to the second quote.

To estimate the performance of the Aquarite cell, divide the instant salinity reading by the actual salinity. If the performance is less than 75%, the cell is failing and it's time to replace it.

Hayward Aquarite SWG - Further Reading

www.troublefreepool.com

To estimate the performance of the Aquarite cell, divide the instant salinity reading by the actual salinity. If the performance is less than 75%, the cell is failing and it's time to consider replacing the cell.

The problem with going below 75% is that the salinity will begin to trigger a low salt warning unless you keep increasing the actual salinity or you can change the cell type to a smaller cell to make it work longer.

What percentage would you recommend replacing the cell?

Can someone go to 50%?, 10%?, 1%?

At 50%, you have to keep the actual salinity at 4,800 just to keep the box reading at least 2,400 ppm, which is the minimum level.

 

[Saturn94]

Also, I generally don’t agree with the guidance that a discrepancy in the salinity measurement should be used as the deciding factor for whether or not a cell should be replaced. I haven’t looked at any of the Pool School articles that talk about that but I think that’s wrong. No SWG is going to measure salinity precisely. It may be an indication that the cell is nearing its end of life but whether or not to replace should be based on the cell working or not. If it’s generating chlorine, then who cares what the salinity readout says.

@Leebo do we have guidance somewhere stating that a cell needs to be replaced based on how erroneous the salinity measure is?? If so, that needs to change.

I know from past experience the AquaRite salinity reading will drop unexpectedly when the cell reaches it’s end of life. That’s why when the K1766 was reading a salt level 800-1000ppm higher than the AquaRite, I thought the 6 year old cell was dying (the previous cell lasted 7 years).

I guess the 75% recommendation is to avoid ending up with very high actual salinity level so when one does install a new cell they won’t have to replace a bunch of water to lower salinity?

 

[JamesW]

Note that this only applies to the Aquarite as it is the SWG that determines salinity from cell performance.

 

[Saturn94]

Note that this only applies to the Aquarite as it is the SWG that determines salinity from cell performance.

Good point for those who may be reading this thread and don’t use the AquaRite.

 

[JamesW]

I guess the 75% recommendation is to avoid ending up with very high actual salinity level so when one does install a new cell they won’t have to replace a bunch of water to lower salinity?

That's part of the reason.

In any case, the 75% mark just helps identify when the cell has begun to reach the end of it's life.

Typically, the cell performs well for years and then it begins a sudden decline as it begins to fail.

If someone wants, they can run it as long as they feel like it's still worthwhile.

At some point the cell might not be able to keep up or you might have to significantly increase the pump run time.

 

[Saturn94]

I just changed the recommendation from the first quote to the second quote.

Hayward Aquarite SWG - Further Reading

www.troublefreepool.com

The problem with going below 75% is that the salinity will begin to trigger a low salt warning unless you keep increasing the actual salinity or you can change the cell type to a smaller cell to make it work longer.

What percentage would you recommend replacing the cell?

Can someone go to 50%?, 10%?, 1%?

At 50%, you have to keep the actual salinity at 4,800 just to keep the box reading at least 2,400 ppm, which is the minimum level.

Wow! At 50% that’s quite a difference.

That can be a real issue for those with water restrictions when it comes time to replace the cell.

 

[JamesW]

It's actually not uncommon for people to keep adding salt based on relying on the box and not realizing that the cell is failing.

The salinity is usually in the 5,000 to 6,000 ppm range when the cell suddenly dies completely.

When the person installs the new cell, they are surprised when the reading is 5,800 ppm and the unit shuts off.

 

[JamesW]

For example:

Replaced cell, still having problems

Good afternoo! I noticed this season I had to bump up the percentage of run time to higher than normal levels to keep up with the needed chlorine production. It also occurred to me that it seemed like I was having to add too much salt for the minimal amount of water loss I had. This week it was...

www.troublefreepool.com

 

[Saturn94]

It's actually not uncommon for people to keep adding salt based on relying on the box and not realizing that the cell is failing.

The salinity is usually in the 5,000 to 6,000 ppm range when the cell suddenly dies completely.

When the person installs the new cell, they are surprised when the reading is 5,800 ppm and the unit shuts off.

That’s what I’ve tried to avoid by testing. At least now I know part of the reason I was getting wonky K1766 results and won’t rely on just that test going forward.

As much as the K1766 is recommended on TFP, I’m surprised there is never a mention of possible interference with metal sequestrants. Had I known this last year, it would have saved me a lot of frustration and expense.

 

[JoyfulNoise]

I think the guidance is fine as a warning sign that the cell is nearing end of life. No one should ever add salt as a method of making the cell work longer. If the true salinity is at the maximum specified for the cell (usually around 4000ppm) and the cell is reporting below its minimum, then it’s done. Time to throw it in the trash. Adding more salt is the wrong answer. For better or for worse, Aquarite cells use an unconventional method for salinity determination and allow a user lots of dials and knobs to fool around with … that’s both a blessing and a curse. And it’s probably one reason why the Pentair’s and Jandy’s decided to go a different design route - just throw the darn thing out a buy a new one and stop trying to squeeze every last ounce of it.

 

[JoyfulNoise]

That’s what I’ve tried to avoid by testing. At least now I know part of the reason I was getting wonky K1766 results and won’t rely on just that test going forward.

As much as the K1766 is recommended on TFP, I’m surprised there is never a mention of possible interference with metal sequestrants. Had I known this last year, it would have saved me a lot of frustration and expense.

Since this issue is a teachable moment for all involved, I’ll suggest to @Leebo that we add some warnings in Pool School about possible interferences.

You might want to check your phosphates regularly and keep an eye on his much sequestrant you are adding. Phosphates aren’t good to have at high levels and 2000+ is high enough to be concerned about. We don’t know a lot about the side reactions that can happen inside an SWG when high phosphate loads are present nor what heavy use of sequestering agents can do. So unless you really, really need to keep using the Jack’s Magic stuff, you might consider dialing back your usage.

 

[JamesW]

I would say for people with a short season, it might be worthwhile to try to finish the season by changing the cell type instead of buying a cell for the last 20 or 30 days of the season.

That way, you can wait until the next year to buy a cell and the warranty does not get used up in the time that the pool is closed.

However, the cells do keep increasing in price, so waiting probably means that you end up paying more.

In any case, I try to give people the best, most complete information and the pros and cons of the various choices so that they can make the best decision for their situation.

 

[Saturn94]

Since this issue is a teachable moment for all involved, I’ll suggest to @Leebo that we add some warnings in Pool School about possible interferences.

You might want to check your phosphates regularly and keep an eye on his much sequestrant you are adding. Phosphates aren’t good to have at high levels and 2000+ is high enough to be concerned about. We don’t know a lot about the side reactions that can happen inside an SWG when high phosphate loads are present nor what heavy use of sequestering agents can do. So unless you really, really need to keep using the Jack’s Magic stuff, you might consider dialing back your usage.

Fortunately, I’ve not had any issues using the Purple Stuff (probably been using it over 10 years) I remember reading something about potential issues when combined with higher calcium levels. Mine is usually around 75-100; I don’t add calcium other than using cal hypo at opening in 2020 and 2021 due to difficulty getting liquid chlorine. I also add boric acid to 50ppm. I understand this significantly reduces pH rise in the cell. Perhaps lower CA + boric acid has protected the salt cell from high phosphates?

Up until now I’ve pretty much ignored phosphates (another TFP recommendation) other than an occasional test out of curiosity. Going forward I’ll check phosphates more frequently to see what the levels are doing. I’ll also see how much I can cut back on the Purple Stuff without stains returning (on the steps usually). Cutting back would also be easier on the wallet…that stuff ain’t cheap!

Do phosphates persist in the water like calcium, salt, CYA, etc, building up over time unless diluted? Or do they break down over time?

 

[JamesW]

If the true salinity is at the maximum specified for the cell (usually around 4000ppm) and the cell is reporting below its minimum, then it’s done.

The minimum is 2,400 ppm. So, 2,400 ppm/4,000 ppm = 60%.

75% is a good general rule to begin to consider replacing the cell and it accounts for some variation in the accuracy of the tests.

I would put 60% as a minimum for replacing an Aquarite cell.

 

[Saturn94]

Interesting, Jack’s says this about the Purple Stuff

“… The Purple Stuff keeps silica in solution while greatly reducing the incidence of cell fouling (scaling) in salt (chlorine) generators...”

In a typical year, I add 2 quarts at opening (early May), about 10-12 oz weekly during the season, and 1 quart at closing (mid October).

Btw, years ago I use to use a closing kit that included a quart of phosphate remover (Phos X brand, says will remove 1000ppb in 20k gallon pool). Of course it would turn the pool into milk. When I uncovered at opening, there would be a layer of white stuff on the bottom that needed to be vacuumed out. Of course vacuuming stirred up a bunch, clouding the water, which took a few days of filtering to clear up completely. It was a mess and a hassle, so I stopped using it.

 

[Saturn94]

I would say for people with a short season, it might be worthwhile to try to finish the season by changing the cell type instead of buying a cell for the last 20 or 30 days of the season.

That way, you can wait until the next year to buy a cell and the warranty does not get used up in the time that the pool is closed.

However, the cells do keep increasing in price, so waiting probably means that you end up paying more.

In any case, I try to give people the best, most complete information and the pros and cons of the various choices so that they can make the best decision for their situation.

You may remember that’s just what I did last year when I thought the cell was nearing the end of its life. Turns out I just needed to add salt, but it’s good to know for future use.

 

[JoyfulNoise]

Interesting, Jack’s says this about the Purple Stuff

“… The Purple Stuff keeps silica in solution while greatly reducing the incidence of cell fouling (scaling) in salt (chlorine) generators...”

In a typical year, I add 2 quarts at opening (early May), about 10x12 oz weekly during the season, and 1 quart at closing (mid October).

Btw, years ago I use to use a closing kit that included a quart of phosphate remover (Phos X brand, says will remove 1000ppb in 20k gallon pool). Of course it would turn the pool into milk. When I uncovered at opening, there would be a layer of white stuff on the bottom that needed to be vacuumed out. Of course vacuuming stirred up a bunch, clouding the water, which took a few days of filtering to clear up completely. It was a mess and a hassle, so I stopped using it.

Silica isn’t an issue. So there’s really not much to that statement other than feel-good marketing hype. All of these anti scaling agents do is hold calcium in solution lowering its ability to scale. But it will also bind up all different metals too. Given how much you are adding, your phosphonate (HEDP) level is probably close to the 10-15ppm recommended level for anti-scaling. As the HEDP is broken down by chlorine, orthophosphate is created. That’s where your 2000+ ppb reading is coming from. Phosphates never leave the water unless they are displaced by fresh water additions. Winter closings, draining and refill lowers the phosphate level in the spring.

Are you absolutely sure you need to keep using the sequestrant? It’s really not something that is needed unless you are getting iron stains.

As for phosphate removers, they should never be left in the pool. They are supposed to be added and then the resulting reaction product (milky substance) is supposed to be filtered out for 36-48 hours and backwashed out of the filter. Leaving the phosphate floc (which is what it is) over winter only causes it to release phosphates slowly back into the water. So that entire process was pointless.

Phosphate scale inside an SWG is what kills it quicker than normal. But, because your CH is so low, your danger of scaling calcium phosphate is minimal.

 

[Saturn94]

Silica isn’t an issue. So there’s really not much to that statement other than feel-good marketing hype. All of these anti scaling agents do is hold calcium in solution lowering its ability to scale. But it will also bind up all different metals too. Given how much you are adding, your phosphonate (HEDP) level is probably close to the 10-15ppm recommended level for anti-scaling. As the HEDP is broken down by chlorine, orthophosphate is created. That’s where your 2000+ ppb reading is coming from. Phosphates never leave the water unless they are displaced by fresh water additions. Winter closings, draining and refill lowers the phosphate level in the spring.

Are you absolutely sure you need to keep using the sequestrant? It’s really not something that is needed unless you are getting iron stains.

As for phosphate removers, they should never be left in the pool. They are supposed to be added and then the resulting reaction product (milky substance) is supposed to be filtered out for 36-48 hours and backwashed out of the filter. Leaving the phosphate floc (which is what it is) over winter only causes it to release phosphates slowly back into the water. So that entire process was pointless.

Phosphate scale inside an SWG is what kills it quicker than normal. But, because your CH is so low, your danger of scaling calcium phosphate is minimal.

Great info, thanks!

Another source of phosphates is our city water. It’s mentioned in the water report they add it to prevent pipe corrosion, but doesn’t mention at what level. I don’t remember if I ever tested it.

Yes, if I don’t use the sequestrant, the stairs, and eventually the liner, over time will slowly develop iron stains (doesn’t happen immediately). Years ago I went through a process with Ben from the old Pool Forum to try to nail down the source of the iron. He had me do a bucket test to check for iron (nothing showed up). The only sources we could come up with are the city water and/or pool salt. I suspect the iron level is low, but just enough to stain given enough time.

It’s odd though. In the spring when I open I do a SLAM and don’t run the SWCG until it’s done and FC is stable. I also bring the pool to SLAM level at closing. Stains do not appear when I SLAM. It seems the stains only start to appear when I run the SWCG. I wonder if the conditions inside the cell when running are causing iron to fall out of solution? There is a return in the stairs and it’s the stairs (white) that show staining first. It takes far longer for any stains to show on the liner (also white now, originally was a light color).