New "mushy" white substance on SWG cell

[stevenfex]

Over the last couple months I have had an issue with mushy white buildup around the ends of my SWG cell plates, which has never happened before. In the past when I would get scaling, before I really held my pH in check and my TA was double what it is now, it would be hard and would take some effort to actually break it into pieces. Now it's just this mushy white grit.

Two weeks ago I cleaned a lot of it off after the check cell light on my Edge 40 panel was on. Now the check cell light is on again, but intermittently it goes off and the SWG seems to operate normally when the light is off.

This cell is only 17 months old so I would think nowhere near end of life. During summer I do run my pump and SWG 24h/day at 1800rpm and the lowest SWG setting.

I have been adding liquid chlorine (10%) as needed for 4-6 weeks now, but have only needed to add about 1.5gal total in that time. Partly because the SWG is still working about half the time, and partly because I have the pool mostly half-covered with a solar cover. Early June is when I started using the solar cover, so this issue has at least correlated with the increased pool temperature.

My pool chemistry is and has been around the following consistently for the past 6 weeks. Before then, I was consistently testing pH/FC consistently and the others every few months. I add MA every time I see the pH even getting close to 7.8 to keep CSI < 0. Ends up close to a gallon of acid per month.

Temp - 86 degrees
pH - 7.5
FC - 5
CC - 0
TA - 60
CH - 425 600
CYA- 20 (adding some soon)
Salt - 3800
CSI using the above is -0.21 -0.07 per poolmath.

I just took apart my DE filter for the first time yesterday, and I am in the process of reassembling now (needed a new standpipe o-ring). If it matters, I use Aquaperl perlite instead of DE. Some observations:

1. Two of the grids had a full layer of sandwiched gunk/media between them. The other grids were consistently covered with a thin layer of gray used media like what I've seen in filter cleaning videos.
2. The grid meshes are all intact, but when I went to pull up the top manifold, it actually came up a bit without the grids. I am thinking whoever last assembled it did not have it set properly to get the thumbscrews snug. So, perhaps some residue from the pool/filter could have made it to the outlet pipe without really being filtered.
3. The pool has been very clear so the filter is definitely still functioning overall. Backwashing the filter does result in murky gray water at first and clear water after 1-2 minutes. Very curious to see what my filter pressure will be after cleaning these grids though.

I'll update this thread after getting the filter back up and running, but I wanted to know if there's any chance the filter could have been the culprit here, like it's letting through some sediment?

Do I just need to keep my pH even lower during summer when the pool gets up to 85-90 degrees?

Does anyone have issues like this while running a VS pump at a low RPM constantly? I wonder if a 3000rpm cycle every day would wash this away.

 

[mas985]

In my experience, the mush is typical with a failing cell. A response from @JoyfulNoise about the same issue:

I would suspect that the ruthenium coating uniformity is quite poor likely with patches of exposed titanium plate. Even though titanium forms a thin oxide layer, it can still conduct electricity to a certain degree. Without the ruthenium coating, the chlorine gas formation will be less favored than the formation of oxygen gas, hydroxide, and hydrogen gas. In that case you’re going to get much higher hydroxyl levels without the acidic effects of chlorine reacting with water to form hypochlorous acid. The higher pH will lead to much greater scale formation which is likely the root cause of all the mineral “mush” you see.

How often are you cleaning the cell with acid? Too frequently or high concentration can reduce the cell life some.

Is the cell still under warranty?

You could trying lowering CSI further to see if that helps. I usually target -0.3 > CSI > -0.6. I find the lower CSI keeps the cell cleaner for longer.

 

[stevenfex]

Also worried about that of course. Before these past two issues with the mush, it's only needed to be cleaned once, maybe twice this year. So since March 2022, it's been cleaned 3-4 times with a 4:1 dilution, only when the check cell light comes on and I see scaling present.

This cell was a replacement of the original cell I purchased in June 2021. With the old cell, I was getting low salt readings constantly with 3600+ salt levels. I actually shipped back my control panel for testing and Circupool sent me a replacement cell after they found no issue with the panel.

I see that CYA can affect CSI as well, so maybe in the future I need to keep that on the high end and be even more aggressive about keeping pH < 7.5.

 

[stevenfex]

Filter reassembled, and unfortunately I think it's just a failing cell after just under two swimming seasons.

I'll get in touch with Circupool but I have some questions:

1. Is there an issue running the SWG 24hr per day even if it's at the lowest setting? Unheated pool so it's off for about half the year.

2. Is there any other chemical that could be in the pool that would cause rapid deterioration of the cell/coating? I've only checked what's in the TF-100.

3. Is cell cleaning 2-3x per year enough to do this? ie. would I have to keep CSI -0.5 to -0.2 or whatever basically 100% of the time so that I ~never needed to clean?

 

[BDY]

Running water through your cell 24/7 will not affect it. The cell will only be “on” for the percentage of time you have it set for. So if it’s set for 10% it will be on only a fraction of the pump run time.

 

[proavia]

Keeping CSI in the 0.00 to -0.30 (negative 0.30) range will minimize scale buildup in the cell.
Cleaning the cell 2-3 times yearly should be unnecessary.
Cleaning the cell with a diluted acid mixture removes a little of the coating on the cell plates - which reduces the longevity of the cell.

Since you don't close your pool, unlike those in the northeast US, you need to maintain the chemistry year round - whether you're using the pool or not. If the water temps are too low for the SWG to produce chlorine, you need to add liquid chlorine. If using liquid chlorine to maintain FC, use the non-SWG FC/CYA chart.
FC/CYA Levels

 

[mas985]

1. Is there an issue running the SWG 24hr per day even if it's at the lowest setting? Unheated pool so it's off for about half the year.

No

2. Is there any other chemical that could be in the pool that would cause rapid deterioration of the cell/coating? I've only checked what's in the TF-100.

Possibly Phosphates. Some believe it has an effect on cell life.

Failing Salt Generators: The Phosphate Connection

When a salt chlorine generator begins to fail it will not produce sufficient free chlorine to keep up with demand. One possible cause is the presence of phosphates in the pool water.

www.aquamagazine.com

3. Is cell cleaning 2-3x per year enough to do this? ie. would I have to keep CSI -0.5 to -0.2 or whatever basically 100% of the time so that I ~never needed to clean?

You can reduce the frequency of cleaning with a lower CSI. Also, if you can avoid acid wash or use a much lower strength, it might help. The only time you should need acid is when the scale is too hard to remove any other way.

I use bamboo skewers to remove as much scale as I can and if there is any left that I cannot remove, I use an acid wash 10:1. It just takes a little longer.

The quality of the cell also has an impact to cell life.

 

[stevenfex]

Keeping CSI in the 0.00 to -0.30 (negative 0.30) range will minimize scale buildup in the cell.
Cleaning the cell 2-3 times yearly should be unnecessary.
Cleaning the cell with a diluted acid mixture removes a little of the coating on the cell plates - which reduces the longevity of the cell.

Since you don't close your pool, unlike those in the northeast US, you need to maintain the chemistry year round - whether you're using the pool or not. If the water temps are too low for the SWG to produce chlorine, you need to add liquid chlorine. If using liquid chlorine to maintain FC, use the non-SWG FC/CYA chart.
FC/CYA Levels

That's pretty much the range I keep CSI in with likely a few exception when the water temp was 90+ and pH closer to 7.8. I'm wondering if that would produce minimal scaling that would then pick up additional material from the filter, prompting me to clean the cell. Still, I can't imagine a few cleanings would reduce a cell warranted for 7 years to fail in less than 2.

No

Possibly Phosphates. Some believe it has an effect on cell life.

Failing Salt Generators: The Phosphate Connection

When a salt chlorine generator begins to fail it will not produce sufficient free chlorine to keep up with demand. One possible cause is the presence of phosphates in the pool water.

www.aquamagazine.com

You can reduce the frequency of cleaning with a lower CSI. Also, if you can avoid acid wash or use a much lower strength, it might help. The only time you should need acid is when the scale is too hard to remove any other way.

I use bamboo skewers to remove as much scale as I can and if there is any left that I cannot remove, I use an acid wash 10:1. It just takes a little longer.

The quality of the cell also has an impact to cell life.

Thanks for the link. I'll look into the phosphate issue and definitely test the levels. I would use the flimsy end of a lomg zip tie to remove as much as I could, but then I would just use the 4:1 acid solution until bubbling stopped. For sure in the future I will reduce the concentration and potentially even just reinstall the cell with minimal scale left on it...

I've dug around quite a bit to see if others have issues with these Edge cells and I can't find any sort of consistent bad feedback on them.

 

[BDY]

Popsicle sticks work too…

 

[stevenfex]

In my experience, the mush is typical with a failing cell. A response from @JoyfulNoise about the same issue:

I searched the forum for this response to try to read the thread where it was, but I can't find it. Any idea?

 

[Rancho Cost-a-Lotta]

SWGs are designed to reverse polarity to shed scale before it begins to build up. I wonder if constantly running the cell on the low setting is somehow interfering with the cell's ability to reverse polarity and allowing scale to build up. Some SWGs don't cycle on/off during a scheduled run to accommodate output settings. Instead, they produce chlorine gas during the entire run, but adjust voltage/current to the cell based on the output setting. Maybe the running at the low setting is not providing sufficient current to clean the cell plates. I checked the manual and it doesn't describe how the unit adjusts output.

My thoughts are just speculation. but there's nothing in your chemistry that would indicate a tendency towards scaling in the cell or anywhere else for that matter. Maybe you can try running the SWG for less time at a high setting and see if it helps. I would call CircuPool/Discount Salt Pool for guidance.

Support: 888-206-9938 extension: 2

Best of luck!

 

[mas985]

I searched the forum for this response to try to read the thread where it was, but I can't find it. Any idea?

That is because it was a PM discussion. Perhaps we can get @JoyfulNoise to chime in.

I have owned my pool over 15 years now and I have found that a CSI >-0.3 is insufficient to reduce scale much. Our fill water has very high CH, TA, PH and the pool has a CH that is normally quite high and currently getting close to 800 ppm. RO or a refill is not too far away.

 

[JoyfulNoise]

Hello … just started reading this one.

Electrolytic chlorine cells, especially the unseparated bipolar types used in pools are subject to weird current density distributions as well as scaling because of the highly alkaline and mineralized nature of the pool water we use. Couple of questions -

Where is the mush concentrated the most, on the edge of the cell plates where water enters or where the water exits the cell?

What are your most reagent CH and TA test results?

Do you run the cell 24/7 on low output or do you target a specific amount of time for the cell to run at higher output?

What is the flow rate while generating?

 

[stevenfex]

Hello … just started reading this one.

Electrolytic chlorine cells, especially the unseparated bipolar types used in pools are subject to weird current density distributions as well as scaling because of the highly alkaline and mineralized nature of the pool water we use. Couple of questions -

Where is the mush concentrated the most, on the edge of the cell plates where water enters or where the water exits the cell?

What are your most reagent CH and TA test results?

Do you run the cell 24/7 on low output or do you target a specific amount of time for the cell to run at higher output?

What is the flow rate while generating?

On the inlet side you can see in the first two pictures in the OP, it's fairly scattered blobs. The build up is not between the plates much except for isolated portions maybe 0.5-1" deep. On the outlet side (pictures 3 and 4), you can see the build up is almost entirely isolated to the plate corners, kind of tucked behind the edges of the plastic interior as it funnels water toward the 2" outlet. There is almost no buildup between the plates at this side. Overall, there was more buildup on the outlet side, but not by a huge amount.

This amount of build up occurred in about two weeks after cleaning w/ 4:1 acid solution. What triggered that cleaning was the check cell light and even more of this mush. I didn't take any pictures that time. The acid cleaning did bubble fwiw.

I tested CH/TA again just now. Embarrassing but I had done the math wrong. I wrote down 21 drops = 425 for CH last time. Today I am getting 24 drops, so CH = 600 which puts CSI at 0.12 for pH=7.7 and 86 degree water. pH was 7.7 right now so I added some acid after testing.

I tested my fill water CH and it's at 200. TA confirmed 60.

SWG is on 24/7 on the lowest setting (12.5% basically). Not sure how to answer the flow rate question. Pump is set at 1800rpm which I increased from 1500rpm previously because the 1500rpm would trigger low flow as the filter got near needing a backwash. Though I bet now with the filter properly cleaned this would be different. My operating pressure now is about 4psi vs. 10psi before cleaning the grids.

 

[stevenfex]

I have owned my pool over 15 years now and I have found that a CSI >-0.3 is insufficient to reduce scale much. Our fill water has very high CH, TA, PH and the pool has a CH that is normally quite high and currently getting close to 800 ppm. RO or a refill is not too far away.

That's reassuring, ha. I keep reading about people never having to clean their cells, and it just seems crazy to me. For me to stay lower than -0.3 with 85 degree water, I'd have to have CYA at 70 and pH no more than 7.4. Holding that pH doesn't seem reasonable, so I think I just need a better way to handle the scaling that does occur, which is probably just physically removing it and then using a very diluted acid solution only if totally necessary. Though this still seems like more "care" than should be required for a cell marketed specifically as a "long life span" cell.

 

[JoyfulNoise]

I’m still reviewing the pictures but I’ll say this - TFP recommends that you have AT LEAST 70ppm CYA when running an SWG. It’s been shown tone and again that pools with SWGs need higher CYA levels.

 

[stevenfex]

Yeah, that part's not unreasonable. I meant holding pH at 7.4 or lower seems unreasonable. I thought CYA was really just an efficiency part of the chemistry, ie. having 70-80 will require less chlorine overall to keep the pool at a good FC level. I had not tested CYA for obviously too long and let it slip to these levels and have a bag on the way now.

Of course this means my SWG will have to run more to offset the higher daily FC loss. But we're not talking being able to drop my 24h/day run time to like 6h/day at the lowest setting just by getting CYA to 70-80 right? Just using those numbers because that's what it would mean if my issue is that I have effectively "used up" the cell in less than two summers by running it all day. Note the user manual for the SWG says 30-50ppm CYA.

 

[mas985]

I meant holding pH at 7.4 or lower seems unreasonable.

Why is that unreasonable?

I thought CYA was really just an efficiency part of the chemistry, ie. having 70-80 will require less chlorine overall to keep the pool at a good FC level. I had not tested CYA for obviously too long and let it slip to these levels and have a bag on the way now.

Of course this means my SWG will have to run more to offset the higher daily FC loss.

Here are some experiments that I ran to determine the FC UV extinction loss under different CYA levels while keeping the FC/CYA ratio the same:

CYA vs UV Chlorine Loss Test Update

Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now...

www.troublefreepool.com

The bottom line is it is non-linear and the higher the CYA level, the lower absolute FC loss so you can actually set the SWG % to a lower level.

 

[stevenfex]

Why is that unreasonable?

This is just going from memory but I recall people noting that pH rises more quickly from lower levels. Paraphrasing here but I've read stuff like "it's better to go from 7.8 to 7.5 more often than drop all the way from 7.8 to 7.2."

I personally just add enough to go from 7.7/7.8 all the way down to 7.2, but I never tried to log the results from that point to see if pH actually was increasing more quickly from the bottom than it did as it approached 7.8. Anyway, I just thought holding below 7.4 would require lots more acid than I currently use.

 

[mas985]

With a TA of 60 ppm it should not rise as quickly. As you keep PH lower, TA will also drop making it even easier to stay at lower PH levels.

But this precisely the reason I invested in an acid dosing system. Given our high evaporation and high fill water CH/TA/PH, I need to constantly add acid to keep CSI in range.