Plaster is like Sandpaper

[Mikes Pool]

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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[PoolDoc]

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.

[Mikes Pool]

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.

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.

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?

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.

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.

Yes.

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

Yes.

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.

Yes.

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

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

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

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.

[PoolDoc]

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

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!

[PoolDoc]

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.

[Mikes Pool]

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.

[PoolDoc]

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?

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.