Plaster is like Sandpaper

Hello All,
So far I have done everything requested from newbies. I have subscribed, liked you on Facebook, and filled out the pool form and ordered the Taylor K-2006. Now I need your help.

This is the fourth year for our pool. It's been trouble free until this year. All of a sudden we have a very rough surface which leaves our feet sore and abraded. After reading many threads on your web site I think it is calcium scale. I don't know how to get a sample of it so I can put it in vinegar (??).

The guy I use to open and close said to put sodium bicarbonate in it to raise the alkalinity up to the max and then the next day add 2 gallons of muriatic acid to bring the pH back down and then use a wire brush on it. Then repeat this process weekly until it is gone. As little as I know about it that just doesn't seem right.

The pH has always been on the higher end 7.8 and above but I didn't worry too much about it. Now, I think that is the cause of my problem. I just ordered the K-2006 today so I went to the pool store with my sample and here is what they came up with:

pH: 7.8
Calcium: 309
Alkalinity: 90
Chlorine: 1.65
CYA: 79
Salt: 3100 (Pentair IC40)

Thank you in advance.

I'm assuming that you have a concrete pool?

(Hopefully, nobody would tell you to use a wire brush on any other type of pool! If they did, they are truly a pool idiot!)

If you have a vinyl or FG pool, it has to be scale; there's just about no other way for the surface to get rough like you've described. Removing the scale from those pool is pretty easy.

If you have a concrete pool, however, it's harder. The problem is the scale is usually calcium carbonate . . . and so is at least some of your pool's surface.

But if it's a plaster pool (Marcite, marble aggregate + white cement), then the other possibility is that it's the opposite of scale; the roughness is the result of low pH for an extended period (or very low pH for a short period) causing the surface to erode.

You can get a pretty good indicator of which it is by examining non-concrete / plaster submerged surfaces. Scale will usually form on metal and tile surfaces as well as on the pool surface. Erosion will be confined to the pool surface. Also scale will be above the original surface; corrosion will penetrate below the original surface.

Post what you find. It will help me if you fill out the pool equipment form, too: http://pool9.net/pf-equip-form

Thanks for the speedy response PoolDoc. I did fill out the pool form, should I do it again?

The pool is a gray plaster. The grit is not on any tile or plastic return surfaces. The pH has never been low. I don't know if it was low over the winter when the cover was on it.
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For some reason, your user name was omitted, but I found it via email address.

If there's no grit on the tile or plastics, you need to take a look underwater with a mask or goggles, and see if it's raised or depressed.

Tell me about the "bubbler" -- what is it, where is it, when does it run . . . and most important, did you maintain a normal (<7.8) pH while it ran?

I'm afraid I may know what happened; telling you my suspicions may help you confirm or deny them:
1. Your 'bubbler' -- presumably some sort of continuous aeration -- ran quite a bit.
2. Because you were a conscientious pool owner, you maintained a proper pH . . . but you didn't check TA all that often.
3. Because the pool industry -- except for my site and a couple of derivative sites -- does not understand how carbonate alkalinity works in pools, no one warned you what happens if you (a) aerate and (b) maintain the pH. This page -- http://pool9.net/alk-step/ -- explains what happens.
4. You ended up running a pool with VERY low carbonate alkalinity, which eroded your plaster, even though the pH was normal.
5. Consequently, you ended up, not with scale, but with corroded plaster.

An inspection from 6" away with goggles will tell. It will be easier if you do so early or late in the day, so the light striking the plaster at an angle, rather than from directly overhead.

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If there's no grit on the tile or plastics, you need to take a look underwater with a mask or goggles, and see if it's raised or depressed.

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I looked at the plaster with goggles and the plaster is pitted but also rough like sandpaper. I took a 1" putty knife to a small area of plaster and I was able to make it smooth but obviously the pits are still there.

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Tell me about the "bubbler" -- what is it, where is it, when does it run . . . and most important, did you maintain a normal (<7.8) pH while it ran?

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The 2 bubblers are in the shallow tanning ledge and run all the time for the "bubbling brook" effect. The pH is in the high range most of the time.

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I'm afraid I may know what happened; telling you my suspicions may help you confirm or deny them:
1. Your 'bubbler' -- presumably some sort of continuous aeration -- ran quite a bit.

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Yes.

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2. Because you were a conscientious pool owner, you maintained a proper pH . . . but you didn't check TA all that often.

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Yes.

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3. Because the pool industry -- except for my site and a couple of derivative sites -- does not understand how carbonate alkalinity works in pools, no one warned you what happens if you (a) aerate and (b) maintain the pH. This page -- http://pool9.net/alk-step/ -- explains what happens.

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Yes.

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4. You ended up running a pool with VERY low carbonate alkalinity, which eroded your plaster, even though the pH was normal.

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I think the alkalinity readings were within range most of the time.

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5. Consequently, you ended up, not with scale, but with corroded plaster.

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It almost seems as though I have both since I am able to scrape the grit off. Is that possible? Chemically speaking.

An inspection from 6" away with goggles will tell. It will be easier if you do so early or late in the day, so the light striking the plaster at an angle, rather than from directly overhead.[/QUOTE]

I read the article at the link you posted about lowering alkalinity but it seems like my numbers are all within the satisfactory range so right now I'm sort of confused. I plugged my numbers into the saturation index and came up with +0.5. If the pool readings taken yesterday are correct and the saturation index is correct and taken with the article about lowering alkalinity, now I'm really confused!

So my questions are:
1.If my plaster is damaged, what can be done, if anything?
2.What do I need to do to get my pool in balance? Based on the SI.
3.Is there a way to remove the sandpaper feel chemically? The pool is too big to do with a 1" putty knife.

Again, thank you for your assistance.

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Originally Posted by Mikes Pool

It almost seems as though I have both since I am able to scrape the grit off. Is that possible?

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Unfortunately, yes. When you erode the surface of the plaster, what's left is much weaker and even friable.

The alk-step article explains what has ALREADY happened to your pool, in an extreme and uncontrolled degree. I was NOT telling you what you need to do!

I first ran into this problem, years ago on pools with UV ozonation and venturi injection of a little ozone and a lot of air. What happens is the aeration from the venturi strips all the carbonic acid (a component of carbonate alkalinity) and thus drives the pH up. If you neglect your pool, and allow the pH to remain high . . . there's no damage. But if you are conscientious, and adjust the pH, you consume remaining carbonate alkalinity by converting it to new carbonic acid. And then the process repeats.

I'm sure, with the popularity of infinity edges, waterfalls, and yes, bubblers . . . this is a very common problem. It's approaching 20 years since I first published an explanation of this. 10,000's of pool users have PROVED that I was correct, and Chem_Geek has published an extremely comprehensive spreadsheet that displays the whole cycle in excruciatingly comprehensive and detailed fashion. But because the pool industry as a whole has never been willing to acknowledge the fundamental errors in the way they've dealt with carbonate alkalinity, the problem continues, victimizing both pool owners and pool builders, who've been mis-instructed.

Unfortunately, the only fix for having REMOVED the top layer of your plaster is to replace it, with either a replaster job, or by refinishing with epoxy or a lesser pool paint.

I have vague recollections of having heard of people sanding pools -- it would be tedious, but if your remaining plaster is thick enough, it could probably be done using flexible diamond disks. I have had some diamond disks that would work, but those pads are no longer sold. I'm sure there's something out there, but I have no idea how much it would cost or how long it would take.

Sorry!

Someone else was asking about sanding a pool, and I had better results when I searched for his info:

I doubt standard sand paper is what is used.

A grinder like this: Bosch 1994-6 9-Inch Large Angle Grinder

with pads like these:
http://www.tedpella.com/Material-Sci...ms.htm#_814_10
http://www.rockstardiamond.com/polis...FRJk7Aod-gcAcQ

You'll need to see what's required to attach those pads to that grinder. Be aware that sanding an entire pool, even with a 9" grinder and diamond disks, is a slow process.

Well Doc, it is what it is. I don't think I want to sand it. We will just have to plan on having it re-plastered. In the meantime I just want to keep the water balanced. We were out of town for the weekend so I checked the water chemistry before we left on Friday. Everything was good except pH. I added 2 pints of acid to bring it down to 7.4. I checked it today (Sunday) and it was back up to 8.0 so I put 3 more pints in it today.

My K-2006 arrived on Saturday so I used that today. Here are my numbers:

Chlorine - 1.0 ppm, combined - 0.0
pH - 8.0
TA - 110
CH - 320
CYA - 90

The Saturation Index was +0.5 and after adding the acid it should have dropped to -0.05. As you can see I am still chasing the pH. Will I have to keep adding acid several time per week? I can't help but feel that something is causing the high ph but as you can see my numbers all are within acceptable limits. Any ideas?
Thanks.

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Originally Posted by Mikes Pool

As you can see I am still chasing the pH. Will I have to keep adding acid several time per week? I can't help but feel that something is causing the high ph but as you can see my numbers all are within acceptable limits. Any ideas?

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Have you turned off the bubblers?

You really cannot run them continuously. If you want to do so, you MUST readjust your chemistry to allow for a terminal pH of 8.0 - 8.2.

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Originally Posted by PoolDoc

Have you turned off the bubblers?

You really cannot run them continuously. If you want to do so, you MUST readjust your chemistry to allow for a terminal pH of 8.0 - 8.2.

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Yes, I forgot to mention that the bubblers are turned off. That is the first thing I did.
Do you agree that my chemistry looks ok?

You need to maintain a chlorine level around 10% of your CYA (9 ppm), so your chlorine is way too low. You'll grow algae at your current level. But use bleach, not your SWCG to shock. Trying to 'boost' or 'shock' using an SWCG leads to greatly reduced cell life.

Your pH is too high; you need to keep it lower. But you may be dissolving pool plaster that's ALREADY softened and weakened. So, I wouldn't go too low. Maybe, 7.6 - 7.8.

BUT . . . you need to inspect your SWCG cell; the plates may need to be cleaned, given all the movement in pH, calcium and TA levels.

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Originally Posted by PoolDoc

You need to maintain a chlorine level around 10% of your CYA (9 ppm), so your chlorine is way too low. You'll grow algae at your current level. But use bleach, not your SWCG to shock. Trying to 'boost' or 'shock' using an SWCG leads to greatly reduced cell life.

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I've never used bleach, is there a formula for how much to use?

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Your pH is too high; you need to keep it lower. But you may be dissolving pool plaster that's ALREADY softened and weakened. So, I wouldn't go too low. Maybe, 7.6 - 7.8.

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Today, my pH is 7.4 after adding acid last night. My alkalinity went from 110 last night to 70 this morning. Is that because I turned the bubblers off? Am I at the point now where I can control my pH by bringing up the alkalinity?

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BUT . . . you need to inspect your SWCG cell; the plates may need to be cleaned, given all the movement in pH, calcium and TA levels.

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I will inspect the SWCG tomorrow.

Your PF is 4.8. Walmart 8% bleach, per gallon, is equivalent to 0.7 lbs of chlorine gas. So 1 gallon will add 4.8 x 0.7 ppm chlorine to your pool, or 3.4 ppm.

Likewise, if you use dichlor (61% available chlorine in some forms), 1 pound would add 4.8 x 0.61 = 2.9 ppm.

I'm not sure why your pH is moving; there are multiple possibilities. Focus on managing your chlorine, keeping your pH between 7.0 and 7.8, cleaning your SWCG. Run things for a week or two so you establish 'normal' patterns.

I am posting my pool readings for the last 11 days. As you can see pH is all over the place. I pulled the SWG and it was pretty clean but I followed the mfg. instructions and acid cleaned it anyway.The water is very clear and I don't see any dust when I brush. Come to think of it, last year when I brushed I would always see dust. That must have been when my plaster was being attacked! Also, last year is when my original Jandy SWG needed replacing. During that time my pool chemistry got out of whack as the SWG quit right before our vacation and I neglected the pool for about a week. It's all starting to make sense now. I feel like I have things under control now but it is driving me nuts chasing the pH like that. Any suggestions on the pH? Am I resigned just adding acid every other day?

As for the chlorine, I read elsewhere on your site that 4.5% of CYA is good for a SWCG pool and you are saying 10%. Why the difference?

One more thing Doc. What are your thoughts on a "No drain acid wash"? My plaster is blotchy now and I was wondering if that would help with the blotchiness and maybe smooth the plaster at the same time.

Here are my pool readings:


Date FC/ CC/ pH/ TA/ CH/ CYA

7/13 1.0./ 0.0/ 7.8/ 110/ 320/ 90/ Added 3 pts. MA

7/14 2.5/ 0.0/ 7.4/ 70/ 300/ 80/

7/15 2.5/ 0.0/ 7.6/ 100/ 300/ 80/ Added 1 pt. MA

7/16 3.5/ 0.0/ 7.8/ 100/ 300/ 80/ Added 1 pt. MA

7/17 4.6/ 0.0/ 7.8/ 80/ 300/ 75/ Rain, no acid

7/18 5.4/ 0.0/ 8.0/ 100/ 300/ -- Added 1 pt. MA

7/19 5.0/ 0.0/ 8.0/ 75/ 300/ -- Added 2 pts.MA

7/20 6.8/ 0.0/ 7.6/ 75/ 300/ --

7/22 6.5/ 0.0/ 8.0/ 100/ 275/ 80/ Added 1 pt. MA

7/23 5.8/ 0.0/ 7.8/ 75/ 275/ --

7/24 6.4/ 0.2/ 7.8/ 75/ 275/ -- Added 1 pt. MA

I wasn't sure if I should make this a new question so I'll just stay on this thread.
I have been monitoring my pool chemistry almost every day since July 13 2014. Since that time I have added 12 lbs. of baking soda and 6.25 gal. of Muriatic Acid. All of my numbers are good:

FC 6.8
CC 0.0
pH 7.8
TA 90
CH 275
CYA 70

My question has to do with my pH. It is always high. As you can see I am continually adding acid. It just seems like a lot of acid. I am wondering if my pH is just normally high and if there is any thing to worry about with a high pH. My K2006 test kit only goes up to 8 so I am not sure how high my pH actually goes. Is there a different test kit that has a higher pH range? How high is too high? Do some pools naturally have a high pH? This is driving me nuts! Any advice is greatly appreciated. Thank you.

You've been adding too much baking soda. Have your TA be lower at 70 ppm. Also consider using 50 ppm Borates. Only add acid to get to around 7.5 pH (not below) and let the pH get to 7.8 or so before adding acid. Also, if you have a short pipe run between your SWCG and the pool, point that return more downwards to help dissolve chlorine gas bubbles because if they outgas that will have the pH rise. The hydrogen gas bubbles from the SWCG also aerate the water which increases carbon dioxide outgassing that raises the pH. Having a lower TA target and higher pH target helps reduce that problem.

Quote Originally Posted by chem geek

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You've been adding too much baking soda. Have your TA be lower at 70 ppm.

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*My TA was around 60 so that is why I added baking soda. Low TA and aeration is what caused erosion of my plaster so I am worried about that and was shooting for a mid-range level.

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Also consider using 50 ppm Borates.

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*What are the Borates for, to lower my TA?

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Only add acid to get to around 7.5 pH (not below) and let the pH get to 7.8 or so before adding acid.

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*My pH generally goes from 7.6 to 8.0 overnight.

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Also, if you have a short pipe run between your SWCG and the pool, point that return more downwards to help dissolve chlorine gas bubbles because if they outgas that will have the pH rise. The hydrogen gas bubbles from the SWCG also aerate the water which increases carbon dioxide outgassing that raises the pH. Having a lower TA target and higher pH target helps reduce that problem.

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*I do have short pipe runs. The returns are aimed so that it barely ripples the surface of the water. What is the correct way to aim the returns? Should I aim all 5 of them down?

Thank you again for your time and expertise.

p.s. I apologize for the structure of this reply. I haven't figured out the tools.

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My TA was around 60 so that is why I added baking soda. Low TA and aeration is what caused erosion of my plaster so I am worried about that and was shooting for a mid-range level.

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It is not just low TA and aeration that can dissolve plaster, but also low Calcium Hardness (CH) and low pH. It is the combination that you want to saturate the water with calcium carbonate. So you can readily have a lower TA level of 60 or 70 ppm if you don't lower the pH as much and you raise your CH level. A higher TA will have the pH tend to rise faster. I'd shoot for 70 ppm and raise your CH as needed. Let's say you plan to keep your pH in the 7.6 to 7.8 range and that you have your CYA level at 80 ppm (to minimize chlorine loss so you can turn down your SWG on-time) and have a minimum FC target of 4 ppm. Assuming 3000 ppm salt, you could raise your CH to 500 ppm to have a saturation index of -0.2 at pH 7.6 and 0.0 at pH 7.8 which should be fine (you could have your CH at 400 ppm and probably be OK since your pH tends to stay towards the higher side).

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What are the Borates for, to lower my TA?

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The 50 ppm Borates are for additional pH buffering that should slow down the rate of pH rise and also prevent scaling in the SWG cell.

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My pH generally goes from 7.6 to 8.0 overnight.

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This is probably a combination of your TA being too high and having the short pipe runs not fully dissolving chlorine gas. The use of 50 ppm Borates will also slow down this rise though won't change the amount of acid you need to add. Having your CYA level at 80 ppm will help because it will protect chlorine from sunlight more even with the FC higher to maintain a 5% FC/CYA ratio (i.e. 4 ppm FC with 80 ppm CYA). Losing less chlorine to sunlight means you should be able to lower your SWG on-time and that will reduce the rate of pH rise since there will be less aeration of the water from the hydrogen gas bubbles and less chlorine gas that escapes.

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I do have short pipe runs. The returns are aimed so that it barely ripples the surface of the water. What is the correct way to aim the returns? Should I aim all 5 of them down?

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I would point the returns that are closest to the pump downwards or diagonally downwards (depending on the type of flow you want). You'll probably need to keep some returns pointed so that you get some surface water motion to be able to move debris to the skimmer.

Thank you Chem Geek. I think you have illustrated how each pool (mine, for example)is different and how the pool store's cookie-cutter approach doesn't work for all pools.

I have followed your advice up to this point;

The TA mysteriously went down to 70. This is after adding baking soda 2 weeks ago to bring it up to 90. I'm glad that it went down on it's own as I understand the process in attempting to lower it. I just hope it doesn't keep dropping.

I increased the CH to 425 from 275.

I adjusted a few of my jets and changed the pump run-time from 14 hours a day to 9 hours a day. I also increased the chlorine output on my SWCG to compensate for the reduced run time. Will this cause an increase in gas bubbles?

Today the pH was 7.8 and the FC was 5.4. CC was 0.0 My CYA is still at 70 but I will bring that up.

The one thing I'm not sure of is the Borates. What is it and with what do you increase it and measure it?

I want to thank you again for taking the time to help me with this and to be a more educated and trouble free pool owner.

I can answer that last one:
You add borates by adding ordinary 20 Mule Team Borax, which we also recommend first for increasing pH (so you have to add acid to control pH).
There are borate test strips which are about the only test strips we recommend. Higher borates inhibit algae and make the water feel softer.

You can add borates by adding a combination (added separately in split doses) of borax and acid or you can buy boric acid and add that instead.

To all of the Pool Forum experts:

I want to give you all a big thank you. For the first time this year I feel like I finally have my pool water where it needs to be and more or less trouble free. Besides the eroded plaster, my big issue was the pH rising constantly. The pH still rises and I still have to add acid but by following everyone's advice on this forum the frequency of adding acid has been reduced by about 2/3rds. The plaster I will deal with at a later date.

The advice from Chem Geek to raise my CH to 500 and to lower my TA to 60 is contrary to what I would have heard from any pool store or any swimming pool publications, but that is what my pool needed.

My first post on this forum was almost 2 months ago. If there is any bit of advice I can give to new subscribers it would be to have patience and to do exactly what you are told to do by the people who are trying to help you. There is no magic bullet. It takes time, patience, and persistence. With everything I have learned about my pool this year I am confident that I will have no trouble maintaining my pool in the future.

Happy Swimming!

Thank you, Mike, for the nice post! Glad you had a good summer and were able to enjoy your pool! :)