White stuff in SWG

[jmcdtucson]

I have white mineral build up on my Intex SWG cells after only a week of operation.
The unit still seems to work fine, but I doubt it will for long.
I've pulled it and currently soaking in vinegar per the manual. But my question is how can I prevent this in the future? We have very hard water and my CH is off the charts.



Here are my test results (note I'm bringing the CYA up).

FC: 4
CC: 0
CH: 500
CYA: 30
PH: 7.2
TA: 130
Salt: 4400

 

[Melt In The Sun]

There are a couple things you can do:

Lowering your TA will certainly help (http://www.troublefreepool.com/content/129-how-to-lower-lowering-total-alkalinity)
Adding borates will also help a lot (http://www.troublefreepool.com/threads/4655-So-you-want-to-add-borates-to-your-pool-Why-and-How)

We probably have the same water as you, and have had success. You'll probably need to drain the pool every 3 years to keep CH below 1000.

 

[RobbieH]

I would have given the same answer you got above.

 

[jmcdtucson]

Thanks. Extensive reading was leading me in that direction. Looks like I have more work to do

 

[RobbieH]

Don't add the borates until you get that TA down to about 70.

 

[SunnyOptimism]

What they said.....

Also, your CH is about the same as mine (400-500) so i'll keep an eye out on my cell when we clean it later this year.

Couple of questions -

1. Have you tried dilute muriatic acid (4 parts water 1 part acid) to clean? Acetic acid will only very SLOWLY dissolve Ca. MA is much better at it.

2. Does your cell do periodic current reversal? It would say so in the manual. Basically it just means the cell reverses the voltage potential on the plates so that each plate sees the same amount of usage. It is supposed to help with keeping scale from building up all on one plate...

3. DO you regularly check your calcium saturation index (PoolMath can calculate it for you). If your number is too positive, then it means you're going to be more prone to scaling and Ca deposition.

 

[jmcdtucson]

Thanks for the advice. Looks like I'm not as off the charts as I thought.

For your questions my fellow Tucsonan Sunny:

#1 - I used vinegar. It worked but did take a an hour or so. Do you know what percent acid solution you start with prior to diluting it?
#2 - The manual only says they have a self cleaning feature but don't go into what that is.
#3 - I hadn't heard of CSI today (not reading carefully enough). I plugged in my numbers and got -0.09. So it's not too bad.

I'll work on getting that TA down then look into borates.

 

[SunnyOptimism]

Thanks for the advice. Looks like I'm not as off the charts as I thought.

For your questions my fellow Tucsonan Sunny:

#1 - I used vinegar. It worked but did take a an hour or so. Do you know what percent acid solution you start with prior to diluting it?
#2 - The manual only says they have a self cleaning feature but don't go into what that is.
#3 - I hadn't heard of CSI today (not reading carefully enough). I plugged in my numbers and got -0.09. So it's not too bad.

I'll work on getting that TA down then look into borates.

The experts (chemgeek, JasonLion, etc) can always correct me here but borates are really a secondary, "nice-to-have" kind of thing, not necessary for proper SWG opration. All borates will do is add to your overall TA (which is why you need to lower TA before adding borates), act as an additional pH buffer keeping your pH swings low and give your water some algae-static property. I plan on adding borates later this season but I'm in no rush.

MA comes in a lot of different grades and concentrations, but I typically use the strongest commercially available product which is 31.45% HCl. I don't believe you can get higher concentrations without it fuming Cl gas. So if you do a 4:1 dilution, then you get ~ 6.29% acid. Most distilled white vinegar is ~ 6% acetic acid. However, acetic acid has a much weaker pKa (acid dissociation constant) than HCl, so HCl is much more reactive to Ca.

Of course, I'd only use a imported balsamic vinegar for my pool

Yes, -0.09 CSI is pretty good. Being positive would be better. Also remember that inside your SWG cell, you are creating both Cl gas AND sodium hydroxide from the salt. The NaOH reacts with the pool water acid to go back to being NaCl but inside the local environment of your cell, the pH will be higher than what's in your pool. SO it's not surprising at all the Ca scales out all over the inside of your cell. Again, the TFP experts can beat me up if what I'm saying is not right...

 

[JasonLion]

Borates are especially good for SWG scaling issues. The conditions inside the SWG are extreme compared to the rest of the pool water. Borates help buffer the extreme PH changes inside the SWG much more effectively than other PH buffers, which helps prevent cell scaling. It is the extreme PH that causes scaling inside the cell.

 

[SunnyOptimism]

Borates are especially good for SWG scaling issues. The conditions inside the SWG are extreme compared to the rest of the pool water. Borates help buffer the extreme PH changes inside the SWG much more effectively than other PH buffers, which helps prevent cell scaling. It is the extreme PH that causes scaling inside the cell.

Now your just making me want to add borates more ....