CSI and PH questions related to tile and grout

[Tuffy]

Hi,
I am noticing some problems with the grout in my 1 year old pool. My pool is a concrete pool covered entirely in 4" tiles with grout in between.When I rub the grout even with my finger if feels slightly slick and I get quite a bit of white flaky powder coming off the grout. I spent a day scrubbing all the grout lines with a hand brush and it is better now but I'm worried this may be due to an imbalance in my pool chemistry. After I was finished scrubbing it turned the pool cloudy from all the grout residue. I let it settle and vacuumed and the pool was clear again.
My normal CSI runs around -0.3 which I understand shouldn't be corrosive to plaster.
FC 3.8
CC 0
PH 7.5
TA 70
CYA 55
CH 410
Salt 4500
Temp 30c
Borates 50

I am in the process of draining some water to lower the CH to around 350 but when I run the numbers using the pool calculator it shows me I would need a PH of over 8 to maintain a CSI close to zero. Does this seem right?
Also what could be going on with my grout other than corrosion?
Any suggestions or information will be greatly appreciated.

 

[Tuffy]

Here is a picture of the pool for reference and a screen shot of the pool calculator.

 

[duraleigh]

Just a guess, but calcium deposits is what it sounds like. Regardless of all poolmath will do for you, it will not fix your pool. Your knowledge and understanding of your pool is what will keep it clear.

I would suggest lowering the CH to around 350 and keeping a sharp eye on pH so it never exceeds 7.5. It may take a month or so, but I suspect your issue will go away.

 

[mas985]

When I rub the grout even with my finger if feels slightly slick and I get quite a bit of white flaky powder coming off the grout.

That could also be the salt. A taste test will confirm. With an SWG, when water gets on the tile and then evaporates, it will leave salt residue. I find it gets worse when I have the cover on the pool. So part of my regular maintenance (couple times a month), I will brush the tile.

 

[Tuffy]

What ever it is calcium or salt it seems to be affecting / depositing only the grout and not the tile themselves. It almost seems like grout is getting soft and dissolving. I'll lower the CH and monitor the PH and hope for the best. I don't think it is salt though as the tiles are always covered by water and this is happening to all the grout in the pool

 

[ping]

Read this thread as it might have some answers for you, http://www.troublefreepool.com/threads/53057-Mosaic-Tile-Grout-Going-Soft.

 

[Tuffy]

Thanks ping that seems to similar to my problem. To give a little more history on my situation the pool is nearly 1 year old and I have maintained it from the beginning. Over the last few months my CH has crept up from 350 to 400 and I have been trying to lower it with new fill water which is around 100. The last round only got it down to 390 so I am aiming for 350. Up until the last few weeks I did not have any problem with grout but I has been a good month since I brushed he walls good. After I noticed the grout problem which is a large amount of dusts and small flakes when rubbed ( even with my finger) I scrubbed the heck out of it by hand. After the the grout seemed ok the a few days later I was getting a similar result when I rubbed it with my finger. I don't have any problems with calcium build up at the water line or any other signed of major buildup. Only the grout. The Ph usually gets up around 8 before I drop it down to 7.5 but I have been doing this since day one also. According to everything I have researched my numbers shouldn't be in a range to effect the grout
Thanks again for the replys.

 

[Tuffy]

Ok I have reduced my CH down to 350. My next question is about TA. I have reduced it down to 100 by acid/ aeration. But when running the numbers with the pool calculator it seems my CSI would be better off with TA of 100 than 80. What is your recommendation on is?

FC 5.5
PH 7.5
CH 350
CYA 40
Salt 4200
Borate 40
Temp 30c
TA currently 100 CSI -0.13
If TA 80 then CSI -0.27

 

[chem geek]

If your pH is fairly stable, then you can leave the TA where it is, but if the pH tends to rise then you can lower the TA to 80 and have a higher pH target of 7.7.

 

[Tuffy]

Thanks chem geek...my ph does rise steadily. Partially due to my SWG I assume. I need to add acid weekly as the PH rises from 7.4 to 8 in that time with a TA around 80 to 90. If I drop my TA to the lower end around 60 would this slow the PH rise. What are the negatives to maintaining the TA on the low end?

 

[chem geek]

If you have the TA lower and don't try to lower the pH below 7.5, then you should use less acid to control the pH. You already have 50 ppm Borates so have pH buffering in your pool. By lowering the TA, you lower the rate of carbon dioxide outgassing. Also, if the pool is exposed to a lot of sunlight, then raising the CYA to 80 ppm and raising the FC target accordingly (i.e. absolute minimum of 4 ppm) then you should lose less chlorine to sunlight and be able to turn down your SWG on-time percentage. That should also help lower the rate of pH rise.

If you find that the lower TA helps, then you can keep the saturation index closer to 0 by having the pH closer to 7.8 and you could have the CH a bit higher at 500 ppm, but I'd only do this if the pH gets more stable. The pH rise could be from other sources, but try the lower TA, higher CYA, and lower % on-time (if chlorine losses are less so that you can do this) to see how that goes.

 

[Tuffy]

Good plan chem geek I'll give it a whirl. Still concerned with the grout which seems to be getting soft, still can't tell for sure if it is build up on the grout or the grout it self getting soft and dissolving . That is the reason I lowered the CH to 350 just in case it was calcium build up.

 

[chem geek]

I don't think it's calcium buildup if your measurements are correct. At least not if it's below the waterline. Above the waterline, evaporation can concentrate calcium carbonate from the water, but below the water line with decent circulation it should be at normal saturation and not over-saturated (again, with your numbers).

 

[Tuffy]

I don't think it is calcium either ....so the million dollar question is what is causing it! I'm starting to pull my hair out on this one.