CLR for Cell Cleaning vs. Muriatic Acid

[panamax53]

I had to replace my cell after about 28 months. The manufacturer sent me one for free.I had been following Jandy's suggested 10% acid bath cell cleaning procedures to rid the cell of calcium buildup. I maintain my pool meticulously and stay within TFP suggested ranges. The CH ranges 375 - 425. Currently 375. Lately I noticed the expected effectiveness of the cell dropping off and I knew the calcium buildup was substantial due to the clear plexiglass enclosure.

A friend of mine suggested using CLR as a gentler cleaner. I have to say it did an excellent job, but it took much much longer. The plates looked different than when I'm done doing it with muriatic acid. I started at 3 in the afternoon with 2 ounces or about a 15 % solution and ended up adding another 2 ounces 6 hours later. When I awoke in the morning the cell and diodes were clean as a whistle. My cell is working as efficiently as it did on day one. I asked the manufacturer if this method might not prolong the life of the cells. They had no comment and said they could only say to use muriatic acid.

One could not realistically expect your typical pool tech to do this. I wonder if the instructions using muriatic acid are to accommodate the pool techs who are pressed on time.

Any comments from the chemists, metallurgists and other such learned members?

 

[mas985]

My last SWG cell lasted about 10 years and would clean the cell with mainly a bamboo skewer and sparingly with <5% MA.

 

[mknauss]

There should be no need to regularly 'clean' a SWCG with acid. Mine has been in service since March 2015. I have done the same as Mark, picked a couple pieces of scale out of it earlier this year.

Maintain your CSI between -0.6 and 0 and you will not have scale buildup in your SWCG.

 

[mas985]

Maintain your CSI between -0.6 and 0 and you will not have scale buildup in your SWCG.

Forgot to mention that. That is probably the most important piece.

 

[JoyfulNoise]

I would avoid using CLR. While it is acidic and removes calcium, the chelating agents in it can make the solubility of all metals a lot higher and result in the removal of more of the ruthenium coating than is preferred. If one has to acid wash an SWG cell, then one should never use a solution more concentrated than 5:1 (water:MA) and only allow that solution to sit in the cell for 30sec or until any bubbling has ceased. These cell plates are coated with a mixed oxide catalyst and they are sensitive to acid etching. Once the catalyst is gone, the cell will no longer produce chlorine at an acceptable level.

I’ve owned an SWG for 5 seasons now and, in all that time, I’ve acid cleaned it twice (with no signs of bubbling so the cleaning only lasted 30sec). And, during that time, my CH has been well over recommended levels with the past three seasons having it at or over 1000ppm. As others have said, managing CSI is the most important variable you can control.

 

[panamax53]

My CSI is normally right around -0.30 . One variable here is my Jandy Product that none of you gentlemen seem to have experience with. Maybe your products are better than what I have? Joyful you wrote cheating agent, I assume you its a typo for chelating? I was terrible in Chemistry, (the lights never went on in that class). Joyful, I do get what you are saying regarding the ruthenium. My instructions say 10% solution for not > 10 minutes. Repeat if necessary. That process does seem to degrade the plates to a point of inefficiency after four to five acid cleanings.

Do any of you think I should aim for CH at the low end of the TFP recommended range of 350 - 450? Would that reduce buildup?

 

[mknauss]

If your CSI is always at -.3 you should not be getting significant scaling in your cell. The polarity switch should be shedding any build up.

 

[JoyfulNoise]

Thanks for the catch, yes I did indeed mean to write “chelating”. Most manufacturers do state a 3:1 to 2:1 ratio of water to acid for cleaning but that is way too strong in my opinion. At those pH levels, the catalyst coating in the SWG plates is going to get etched off pretty quickly. In my opinion, the least concentrated acid solution should be used (1% to 5% is more than sufficient) and it should only be used if visible scale is present and bubbling occurs during clean. In the absence of effervescence, the solution should be immediately discarded and the cell rinsed. There are other types of calcium scale (sulfates and phosphates) that cannot be removed with acid and so leaving the cleaning solution in the cell will only damage the catalyst and not touch the scale.

I can see from your signature that your theoretical cell output is about 0.2ppm/hr. So that would mean you need to run your pump and SWG at around 10 hrs per day to keep up with standard chlorine loss. Is that about right or are you running longer than that?

 

[panamax53]

I run 15 hours a day in the summer to keep the pool clean from hordes of gnats and in order to run my cell at a lower %. I use the Pool Math App and test for FC nearly every day. IF all chemicals are close to optimal, which for me is FC 5-6, pH 7.7, CH 375ish, NaCl 4000, TA 60 and CYA 75 - 80 a sunny day takes out 1.5 -1.75 ppm. Often it is more like 2 to 2.5 ppm. A cloudy day has taken 0.5 ppm with those readings. If it' Those are without any swimmers. f

The polarity switch may not be performing optimally. Ok... I wonder if there is a way to test that? I'll give Jandy a call. The diode in the middle of the cell was heavily caked and took the longest to clean... that might mean something to a smart tech at Jandy.

 

[JoyfulNoise]

When the cell is running, the pH inside the cell is always going to be higher than the bulk pool water. In a worst-case scenario it could go as high as 10. I’ve never really calculated it because there are a lot of assumptions involved but it is not outside the realm of possibility that the local CSI inside the cell gets very positive. One chemical technique for controlling pH rise inside the cell is to add borates to your pool water as they act as a buffer against high pH and can limit the pH rise quite strongly. The downside to using them is that your pool water will require a higher dose of acid to lower pH when needed (but, your frequency of acid additions should get longer so the net result is the same amount of acid is used). I personally use borates in my pool and my CH has been as high as 1500ppm without issues (believe men though, you do not want to have a CH that high).

 

[panamax53]

Too many cats drinking from my pool. Adding borates might help get rid of them, but my wife would kill me. The local pool tech is mad at me for teaching my neighbors TFP techniques. " I have 20 years experience and never heard of this approach." Sorry you're so stubborn guy. In the grand scheme of things buying another cell is not such a big deal for me. It's kind of a pain, but I can easily afford it.

Thanks for all your thoughts on the matter. Praise the Lord and pass the bleach!