Scale Removal

[ssummer]

I'm hoping somebody can give me some advice. Our pool is about 4 years old. Last year, I relented and had the pool acid washed due to some excessive calcium scale build up on the walls.

This year, after opening the pool, the entire bottom surface appears to be covered in scale. It's gone from a very smooth surface to it being so rough that it cuts up the kids' feet when they are in there. It’s not very visible (and I do have a dark plaster), so is it calcium scale, or something else? Also, there were no scale deposits on the SWG when I disassembled that at the beginning of the season.

I am religious with testing and maintaining the pool chemistry, with the only thing that ever really gives issues being the pH. It seems to constantly rise on me, forcing me to put muriatic acid in 1-2 times per week. I’m assuming that the pH creep over the winter months is what caused the scale issue to begin with.

So, how do I remove this scale, whether it’s calcium build up or something else? I don’t want to do the acid wash again, for fear of limiting the life of the plaster. Will relentless brushing do the trick? Will something like ScaleTec or Natural Chemistriy’s ScaleFree help, or are those more for prevention?

Lastly, how do I prevent this from re-occuring…apparently I must be doing something wrong.

Any help is appreciated…here are my latest water test results, which have been consistent for the last 4-5 weeks:

FC – 4.0
CC – 0.5
pH – 7.8
TA – 60
CYA – 60
CH – 280
Salt – 3380
CSI - -.26

 

[pooldv]

You are on the right track. Keeping CSI negative, -0.3 to 0, will prevent scale. Temperature affects CSI so you need to recalculate as the water temp changes.

To get rid of the scale you have two options other than another acid wash. You are correct that an acid wash is very aggressive, removes a layer of plaster and will reduce the life of your plaster.
Option 1, least aggressive, lower your CSI to -0.8 to -0.6 and brush often with a stainless steel brush. This is normally a slow process but will probably work faster in your pool since the scale is new.
Option 2, more aggressive, do a no drain acid wash following this process, The Zero Alkalinity Acid Treatment

More here, Pool School - Calcium Scaling

 

[ssummer]

Thanks for the advice pooldv.

The no drain acid wash sounds interesting...a couple of questions about it. (1) Other than adding the acid, what is required for that week of the acid wash (daily brushing?), (2) Is the pool safe to go in during the no drain acid wash, (3) any particular method of bringing the TA back up after the no drain acid wash?

And a few other questions not specifically related to the no drain acid wash...(1) Is using a stainless steel brush daily ok for the pool, or will it result in gouging of the surface?, (2) I do believe that this is the result of the plaster job, and not water chemistry maintenance...I suppose though that there is no way to prove that and hold them accountable. Is there anything I can do to at least keep this from happening again after I get it off? Or, due to the plaster job is it inevitable that it continues to occur?

Oh, and regarding your first option...any recommendations as to how best to lower the CSI that low to be most effective? And how long would you keep it that low?

Thanks again! I really appreciate it.

 

[pooldv]

If you feel like it is a plaster problem or installation problem then feel free to contact SGM and file a warranty claim. I would expect them to be very responsive, most major pool plaster companies are. http://sgm.smod.us/smodMain.php?sys=pub&pub=wif2

If your issue is calcium scaling then I am not aware of any plaster issues or installation issues that would contribute to scale or perpetuate it. Calcium scale is nearly always a water chemistry issue in my experience. But, I always have something to learn.

My personal experience and observed experience with others is that a slightly negative CSI, -0.3 to 0, will always prevent calcium scale in a pool. Our water has high scale potential and we have scale in coffee pots, showers, etc. A few years ago we started getting scale build up along the tile line. Keeping CSI negative removed the scale and it has not returned for 3 years. It also has kept the SWG scale free. The SWG cell is starting pool season 5 and has never needed to be cleaned.

Plaster is fully cured after 1 year and a SS brush is fine to use. Focusing more on places with scale will be helpful while there is an acid bath and or very low CSI.

No, it is not safe to swim during an acid bath. It is safe to swim when
FC is above minimum and up to shock level for your CYA, [FC/CYA][/FC/CYA]
Ph is between 7.2 and 7.8
and the water is clear

CSI is most easily controlled by tweaking PH and TA. But, there are many contributors to the CSI calculation in Polmath. PH, TA, CH, temp, borates, salt and probably more. It is important to enter all test results into Poolmath for accurate calculations.

Baking soda raises TA. Soda ash raises PH and TA. More here, Pool School - Recommended Pool Chemicals