Heavy scaling on the plates of my cell.

[Gregadaka]

I replaced my aging cell just two months ago. I got the replacement from the Salt Pool Guys.
The scaling is so much that I don't think it's generating chlorine anymore. Even the old worn cell didn't scale this badly. I contacted the Salt Pool Guys and all they said was that the high pH maybe responsible. Any ideas anyone?

 

[JJ_Tex]

I see you have pool math, but it doesnt appear you are tracking CSI. Turn that on and have it calculate a CSI for you. You will want to have a slightly negative CSI to keep the scale off.

 

[ajw22]

Your high TA is a problem and causing the scaling in your cell.

What is the pH and TA of your fill water?

TA - Further Reading

www.troublefreepool.com

Why Should TA be Lowered with a SWG?
Usually a TA on the high end is fine if the pH is stable. However TA does need to be adjusted down with an SWG. The problem is, INSIDE the cell, the CSI is very different than in bulk pool water.

With high TA and aeration from the bubbles the SWG creates, you'll get faster pH rise inside the cell and so there's more potential for scaling. With current reversal, the cell tends to stay clean but you'll get more snowflakes out of the returns. Calcium hardness is only one part of the equation.

If the SWG cell pH rises much above 10 (and it can easily do that) and if there is sufficient levels of carbonate ions available (CO3--), then you will get calcium carbonate precipitation. The higher the TA and pH, the more carbonate anions are available.

Borates are particularly helpful preventing scale in a SWG because the pKa for boric acid / borate anion buffering is approximately 9. That essentially means you get the maximum buffering capacity at a pH of 9 and that tends to hold down the pH rise inside the cell. Keeping the pH below 10 in the SWG cell reduces the risk of calcium and magnesium scaling (insoluble magnesium hydroxide precipitates at a pH of 10.2 or so).

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

 

[Rattus Suffocatus]

Yeah... TA. I'm fighting that right now. I'm adding acid every single day now and am starting to question if, in my case, the SWCG was actually worth it. Probably still is, because I hated hauling bleach.... I don't want to add borates because of my dogs thinking the pool is a better water bowl than the ones in the house, so I just fight it. I suspect I will need to clean and replace the cell more frequently than most people.

If you don't have a risk of pets or people drinking the pool water than adding Borates probably would help a lot. I might still try a small amount in the future if I don't get it under control next year.

I had my cell scale up completely in three months even with a slightly negative CSI. (But 130 or so average TA.) It's because I have very high TA fill water but close to neutral pH. The struggle is real.

 

[Gregadaka]

Your high TA is a problem and causing the scaling in your cell.

What is the pH and TA of your fill water?

TA - Further Reading

www.troublefreepool.com

Why Should TA be Lowered with a SWG?
Usually a TA on the high end is fine if the pH is stable. However TA does need to be adjusted down with an SWG. The problem is, INSIDE the cell, the CSI is very different than in bulk pool water.

With high TA and aeration from the bubbles the SWG creates, you'll get faster pH rise inside the cell and so there's more potential for scaling. With current reversal, the cell tends to stay clean but you'll get more snowflakes out of the returns. Calcium hardness is only one part of the equation.

If the SWG cell pH rises much above 10 (and it can easily do that) and if there is sufficient levels of carbonate ions available (CO3--), then you will get calcium carbonate precipitation. The higher the TA and pH, the more carbonate anions are available.

Borates are particularly helpful preventing scale in a SWG because the pKa for boric acid / borate anion buffering is approximately 9. That essentially means you get the maximum buffering capacity at a pH of 9 and that tends to hold down the pH rise inside the cell. Keeping the pH below 10 in the SWG cell reduces the risk of calcium and magnesium scaling (insoluble magnesium hydroxide precipitates at a pH of 10.2 or so).

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

Thanks so much! I'm going to work on getting the T/A down. How do I get the scale off the cell? Should I use dilute Muriatic acid?

 

[ajw22]

Your signature does not say what manufacturer and cell type you have.

There should be manufacturers directions for cleaning the cell.

 

[Rattus Suffocatus]

Your signature does not say what manufacturer and cell type you have.

There should be manufacturers directions for cleaning the cell.

^^^This is the correct answer.

In general you dilute muriatic acid down 1:5 to 1:10 with water (acid added to water and not the other way around ever!) and then either use a cleaning plug or a bucket and submerge the cell. Some cells actually have plates that will come out of the cell... so check your manufacturers instructions. For those, you clean the same way but you remove the plates from the housing.

The recommended ratios of acid to water are different for different manufacturers, so it's good to check. (Though I would always go weaker than suggested by a little bit). You want to only leave the cell in as long as the manual specifies. (Usually about five minutes.) If it's still scaled up, hit it with a hose thoroughly and then put it back in for that same maximum time until it's clean. Be careful if you try try to chip off scale from the plastic pieces that you don't scrape the titanium plates at all.

It's not difficult. You do want to try to avoid using cleanings like this as a substitute for proper water balance. The less you have to do this, the longer the cell will last in theory.

I would inspect the cell to see the level of scale in it. If it's "not bad" then wait a while before you clean it. If your unit estimates salt level you can use the number going down compared to a proper K-1766 test as a estimate of the scale level. If you can read current on your unit, a dropping level usually means scaling as well.

If it's a Circupool unit, there is a "help" section that describes the process on their website better than the manuals do.

Regardless, you want to do the cell descale as sparingly as possible. Good luck. I know the struggle is real. I know from my meter readings my cell is starting to scale again...I would be much happier if I didn't have to descale twice in a season.... I will have a shorter cell life the way it's going...

It's sad, but I already see a difference in scale on the solar cover and tile line because I've been fighting down the TA and I still have a ways to go, honestly. Much less already. And starting off my pool looks better than 90% of the neighbors do because of TFP.

 

[ajw22]

Use a popsicle stick to knock off of the plates as much of the scale that you can before you hit it with a MA solution. In the future if you catch it early enough you can clean off the scale with a stick and not reduce its life with a MA bath.

 

[Rattus Suffocatus]

A plastic stick is even better. Be very careful not to scratch the plates.

I admit, I did a little bit of that with mine. If you soak and spray and soak and spray a lot of time you can break off the chunks with just the water spray though. Be careful is you use any physical force. I used a tie wrap on one spot on mine that was stubborn, last time as a poker, but I didn't/don't want to recommend it do to the chance for damage.

 

[Gregadaka]

Thank you so much guys! Such valuable information. I'll check the manufacturers' instructions for cleaning the Digital Nano Cell, then go ahead and get it done...

 

[Gregadaka]

Rigged up an aerator...
BTW, what's the ideal TA? The TFT kit says 90-100 for a SWG pool. Id that right? My TA today is 260...

 

[mknauss]

BTW, what's the ideal TA?

TA - Further Reading

www.troublefreepool.com

Any TA that allows your CSI to be slightly negative to reduce scaling in your SWCG and allows the pH to remain relatively stable.

 

[Gregadaka]

I've been at it for a couple of weeks now. I've dropped the pH to as low as 6.4 twice in the last month or so, using Muriatic acid. It's risen to 7.6 now. I've been unable to get TA lower than 110. TA is now 140, FC has fallen to 1 and the csi is 0.03. When I increase the FC, it increases the TA. If I drop the pH to "dangerously" low levels like 6.4, I can keep the TA low. This is unsustainable...
What do I do now? Borates?

 

[mknauss]

Raising your FC does not add alkalinity to the pool water. Only a chemical or high TA fill water can add alkalinity to the pool.

Do not lower your pH below 7. Lots of damage can be done to equipment with sustained low pH.

 

[ajw22]

What is the TA of your fill water?

You have an autofill?

 

[Gregadaka]

Raising your FC does not add alkalinity to the pool water. Only a chemical or high TA fill water can add alkalinity to the pool.

Do not lower your pH below 7. Lots of damage can be done to equipment with sustained low pH.

I agree about the low pH being damaging to the equipment. But, I thought Bleach (sodium hypochlorite) is strongly alkaline when dissolved in water.

 

[Gregadaka]

What is the TA of your fill water?

You have an autofill?

Just checked. Our tap water has a TA of 60.

 

[ajw22]

Just checked. Our tap water has a TA of 60.

If your fill water has a TA of 60 how is your pool TA getting to 160? And you say it has risen from 110 to 160?

Have you added any alkalinity increaser, baking soda, borax, soda ash or washing soda to the pool?

 

[mknauss]

But, I thought Bleach (sodium hypochlorite) is strongly alkaline when dissolved in water.

Sodium Hypochlorite is pH neutral and adds 0 alkalinity to the pool water.

You are adding alkalinity from some other product. What all are you adding to your pool water?

 

[Gregadaka]

If your fill water has a TA of 60 how is your pool TA getting to 160? And you say it has risen from 110 to 160?

Have you added any alkalinity increaser, baking soda, borax, soda ash or washing soda to the pool?

A couple of months ago, I bought Muriatic acid, thinking it was the same as CYA... I had my ignorance corrected on this forum - but by then, the pH was 6.2. I fixed the pH with 6 lbs sodium Bicarb (Arm & Hammer). Could that be the problem?