SWG Calcification

[GeoQuack]

Firstly, thanks for these forums. I have learned almost everything I know about my pool here. Bought the house in Feb, pool just stating to go green, but with the info here and pool Calc got it back easily and have not looked back.

But have a problem with the salt cell growing calcium rapidly and spitting it into the pool if not cleaned every week. My pool and test details follow:

Pool plaster 44000 litres, zodiac lm2 30 SWG, manual cleaning (so far)

Test
TF100 not avaliable in Australia. I have been using the one from clearchoicelabs.com.au it does have a fas-dpd chlorine test and hopefully is similar to the Taylor's 2006.

Today's results
pH 7.8, FC 8, CC 0, TA 85, Ca 300, Cya 80, Na 4200, temp 14°C

Pool Calc says that this is balanced and is not likely to either form scale or erode the surface. As the weather warms up I will need to lower the pH as it changes more with greater swg use and these two things mean that the water would became errosive and I should bump up the Ca a bit but my eyes are saying the opposite is the problem.

Very interested in any thoughts or advice.

 

[cowboycasey]

Welcome to TFP

That is a great kit.. Your CSI is at -0.31 and that is a good place for the SWG.. As the temp rises your CSI will rise... I know my SWG has some scale on it but very little and when it changes polarity it comes right off (not in chunks)

Has it always done this or is this a new install, with your temp below 60 degrees (14 C) it is probably not working at the level it will when the temp rises.

 

[ping]

Welcome to TFP!

Make sure that the system is switching the polarity, I believe the manual should let you know how to do this.

You can add 50ppm borates which will help with preventing some of the scaling.

Lower the pH to 7.6 and see if the scale still forms as fast.

 

[pooldv]

Shifting CSI to the negative side should help with scaling. Between -0.3 and 0 is best.

 

[ping]

Shifting CSI to the negative side should help with scaling. Between -0.3 and 0 is best.

His number is already -.31 so there is something else going on here. My first guess is the pH is higher than 7.8 since it is very difficult to read pH above 7.8.

 

[pooldv]

Casey's post says 0.31, not -0.31. Yes, pH could be above 7.8

 

[cowboycasey]

Casey's post says 0.31, not -0.31. Yes, pH could be above 7.8

Early morning post it was -0.31 .... sorry about that, changed...

 

[GeoQuack]

Has it always done this or is this a new install, with your temp below 60 degrees (14 C) it is probably not working at the level it will when the temp rises.

It has done it ever since I got the water relatively in balance after moving into the house. (Largely thanks to lurking on this forum.) When I got the pool it was just starting to go green. The pump was running for 14 hours a day, the chemistry was something like FC 1, CC 1, pH 8.2, TA 100, CH 150, CYA <30, Salt 1000.

Since I got the calcium up to a level recommended for a plaster pool I have had trouble with the SWG throwing off chunks of calcium into the pool. In the cool weather it is producing enough chlorine with the pump running 1.5 hours per day. BTW there is no scaling anywhere else in the pool.

Welcome to TFP!

Make sure that the system is switching the polarity, I believe the manual should let you know how to do this.

You can add 50ppm borates which will help with preventing some of the scaling.

Lower the pH to 7.6 and see if the scale still forms as fast.

I have put a multimeter on it and have not detected a polarity change. The manual says that it should be self cleaning. Do you know how often it should change? Is it 50% each way or just a brief period in the reverse direction?

I am planning on adding borates but was waiting until I sorted out this issue. Maybe I'll give it a try.

There does not seem to be a difference at a pH of 7.6.

His number is already -.31 so there is something else going on here. My first guess is the pH is higher than 7.8 since it is very difficult to read pH above 7.8.

I think my pH is 7.8 as when I add the amount of HCl acid recommended by pool math to lower it to 7.6 the pH does go to 7.6. I have thought of lowering the pH more to try and fix this problem, however, with the pool currently quite cold, my CSI is correct with a pH of 7.8. I was planning on lowering the pH as the pool warms up as this seems to be the easiest parameter to change that contributes to CSI. With the current chemistry and temperature, at a pH of 7.6 the CSI is -0.5 and at 7.5 it is -0.6.

Thank you everyone for your help,

GQ

 

[ping]

To avoid the issues you are having during the cold water months it might be best to turn off the SWG and use liquid chlorine instead. You will only have to add once a week at most I'm guessing. Once the water warms up you will then be able to drop the pH and you shouldn't have issues with the scaling.

 

[GeoQuack]

I have added HCl to drop the pH to 7.6 and the problem seems to have improved. How much of a problem will having a CSI of -0.5 be?

Also, does anyone know how often and for how long the polarity of the salt cell is supposed to change?

 

[pooldv]

That is a little too aggressive over the long term, months to years. Increase CH to 350 to compensate.

 

[GeoQuack]

As an update, there was something wrong with the salt cell or control system. The transformer for driving the salt cell in the controller box died. Because it wasn't that much more expensive to replace the whole system (new control box and salt cell), I did that. I haven't changed the pool chemistry, but the new system is not getting any scale build up on it.

Thanks for your help everyone.