Plaster stains on new salt pool w/high alkalinity

Stains on the pool surfaces, pool equipment
or on the swimmers, or off-color swimming pool
water. Discolored but clear pool water.
bnsfengineer
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Joined: Mon 20 Apr, 2009 11:07
My Pool: 18x36 built 2008 plaster salt system
Location: So. Cal.

Plaster stains on new salt pool w/high alkalinity

Postby bnsfengineer » Mon 20 Apr, 2009 11:50

Help....I have had three pools before and this is my first one with a salt system. Iam always adding acid and when Ive asked advice from my local pool store their response was with a salt system you substitute adding acid instead of adding chlorine.My chlorine level is generally perfect but ph is continually high along with alkalinity being close to 190. My next problem is now I have staining on bottom of pool and the best way to describe it is it looks like dirt blew in the pool and the sweeper never picked up.Ive tried a small wire brush but it does nothing. Iam guessing these stains are from the high alkalinity. What can I do without draining pool and acid washing...pool is only 10 months old. A friend told me to keep adding acid until I reach about 60 ppm alk and that may help leach some of the stains back out ? ?


chem geek
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Plaster stains on new salt pool w/high alkalinity

Postby chem geek » Mon 20 Apr, 2009 22:00

Read more about Calcium Scaling and how to Lower Total Alkalinity . For the latter, you don't just add acid, but must add acid AND aerate the water, all at lower pH.

Since you have an SWG, you should also read Water Balance for SWGs .

Richard
chem geek
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Plaster stains on new salt pool w/high alkalinity

Postby chem geek » Wed 22 Apr, 2009 02:14

I assumed that because of your high TA caused scaling. Normally scaling is off-white, but sometimes it can look gray.

It's also possible you have metal stains, possibly from high pH since the high TA and use of the SWG would tend to make the pH rise. If that's the case, then after lowering the TA and getting a handle on the pH you can remove the metal stains as described here mostly using ascorbic acid.
bnsfengineer
Pool Newbie
Pool Newbie
Posts: 4
Joined: Mon 20 Apr, 2009 11:07
My Pool: 18x36 built 2008 plaster salt system
Location: So. Cal.

Plaster stains on new salt pool w/high alkalinity

Postby bnsfengineer » Wed 22 Apr, 2009 10:25

I get mixed advise on this but have to ask simple question. Do you add acid when pump off and if so how long do I leave off before running. Leslies and others have always told me to never add unless pump is running. I was told as long as PH is slightly high continue as needed with adding acid even if every other day. Is there a rule of thumb not to add too much at one time? Again I have been told two different stories. No more than a quart at a time and a Pool guy said as long as you pour in different areas you should be able to add a gallon if necessary with pump off ??? Also do you dilute before adding? :o
chem geek
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Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Plaster stains on new salt pool w/high alkalinity

Postby chem geek » Wed 22 Apr, 2009 12:44

You should never add acid to the pool with the pump off. That sounds like the "slug" or "acid column" method of reducing Total Alkalinity (TA), but that does not work (see this thread ). The way you lower TA is through acid addition and aeration of the water all done at lower pH. You should add acid slowly over a return flow with the pump running, preferably at the deep end especially if you have a floor drain. After adding the acid, you can lightly brush the side and bottom of the pool to ensure thorough mixing. You never add acid to the skimmer.

The only time you add chemicals to the pool and turn off the pump is with flocculant products (and sometimes phosphate removers if there is a lot of phosphate).

You can use The Pool Calculator to approximate dosages for adding acid to get to a low pH (probably 7.0, if 6.8 is the lowest reading in your pH test).
Guest

Plaster stains on new salt pool w/high alkalinity

Postby Guest » Fri 11 Sep, 2009 20:21

It is the high PH that has caused the stains. PH goes 8.2 and over then stains looking like dust will appear. I have salt system and fight same issue with chem. When PH goes over 8.0 I add acid 1 gallon ( 1/2 at a a time mixed in 5 gal bucket with water in deep end then brush) I keep Alk around 140-160 to buffer PH rise. The higher Alk is the more acid it will take to move PH. I just get used to banging my head against the wall as on thing changes the other. I wish PH could be changed without affecting Alk. But the stains are from PH going high.

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