Dark spots/stains on pebble finish

[mdvcoder]

I have a problem with my pebble finish - random dark spots on the bottom, which looks like pebble discoloration. I think I've had this for a while, but I believe it became worse recently with more darker spots appearing. I've attached a few photos if that helps.

Here is my TF-100 results:

FC 20
CC 0
PH 7.5 (diluted pool water with distilled water to get a more accurate reading as suggested on the forum)
TA 180
CH 650
CYA 180-200

I did overnight FC loss test and it showed zero FC loss. Also, I put a chlorine tablet on the stain for a few minutes and noticed no color change. So, I guess it is not algae or other organics. Also, did a vitamin C tablet test by rubbing the tablet against the stain - no color change either.
Not quite sure what it is, so any help is greatly appreciated.

 

[onBalance]

You might want to try using a (pint size) plastic squeeze bottle and fill with regular muriatic acid, and then squeeze the acid onto the stained area to see if that removes the discoloration.

 

[tstex]

I had a lot more issues w my pebble-sheen finish then what I see w yours.

What my installer did was a no-drain acid wash to bring the TA to near zero in increments and slowly, w 2 circulation pumps. The goal is to more uniformly cure the plaster. I would first bring down your pH to 7.2 which is a good start. the post from onbalance re squirting M-Acid right to the spot is trying to do the same thing, but I am not sure how effective that will be considering it will get real diluted so fast. The PS Installer added 6-8 gallons of muratic acid over 2-3 days and ran 2 circulation pumps to keep it moving throughout the pool.

How old is your psheen/plaster since it was installed? Here's a link that describes the process and provides some cautions too.

The Zero Alkalinity Acid Treatment - Pool Genius Network

Good luck,
tstex

 

[mdvcoder]

Thanks for the suggestions.
The pool was built about 2-2.5 years ago. I bought the place about a year ago, and I think there was already some slight discoloration, but it definitely got worse over the past year. I do have the contact for the installer, so I guess I can give him a call.
Btw, does anybody know what is causing the stains and whether this can be avoided?

 

[boston62]

Is it just me, but your pool balance seems way out...or am i missing something?

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[mdvcoder]

Is it just me, but your pool balance seems way out...or am i missing something?

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Agree, planning to do a partial (or maybe full) drain. The previous owner was a Trichlor tablets user, I used them for a while also (now switched to liquid chlorine), so that explains high CYA. High CH probably comes from continuous addition of tap water (there is quite a lot of water lost due to evaporation here in Southern California). My tap water has 125-150 CH level. So, draining should help both of these. Not sure why TA is that high. Could any of that be contributing to pebble staining/discoloration?
Thanks.

 

[onBalance]

Generally, out of balanced pool water does not cause isolated or blotchy discolorations. Yes, your water is hard, but may not be the problem with causing the discoloration. I am not sure that enough time was given with the Vitamin C or chlorine tablet test to determine a good diagnosis. That is why I suggested a muriatic acid test. The discoloration may be a topical stain (which can be remedied), or it could be a discoloration within the plaster surface itself (which is almost always impossible to remove). That is what needs be to determine with the suggested tests.

Also, plasterers often incorrectly suggest doing "no-drain" or acid bath treatments to remedy all problems. As the Zero Alkalinity article states, it also harms the plaster surface as as end result. Subjecting a plaster surface with acid does not "uniformly cure" the plaster in any way, and plasterers are wrong in suggesting that. Uneven discolorations are generally a workmanship issue or material problem.

 

[mdvcoder]

You might want to try using a (pint size) plastic squeeze bottle and fill with regular muriatic acid, and then squeeze the acid onto the stained area to see if that removes the discoloration.

I tried that today and it didn't have any effect.