Residual Plaster Dust...or is it scale?

[TXFlyGuy]

This is a tough one! I built the pool myself and admit the start up was not properly done, i.e., not brushed often enough during the first few weeks of curing.
The pool is 5 years old and now looks better than ever with the exception of a few random patches of a milky gray coloring on the pool floor. Previously, this milky gray coloring was widespread over 100% of the pool. I recently performed a no drain acid wash for 4 days in which I shut the system down, lowered the PH to 4.0 and the total alkalinity to zero. The pool was brushed religiously 6 or more times a day. Now, 80% of the pool is in perfect condition, except there is still about 20% coverage of the off-white coloring. These few remaining patches are very stubborn!
I have now added a combination of Scaletec & Beautec in hopes of fixing the remaining gray patches. The plaster is Stonescapes Tahoe Blue, and now is a very dark color...what I would call a midnight blue. And the water is absolutely sparkling crystal clear!
The water has been always near perfect in chemical composition, and the CH runs between 250 - 280.
I was hoping to avoid doing a total drain and acid wash due to the cost which would run $675 including the cost to refill the pool, plus the additional cost of chemicals.
I actually think this is leftover plaster dust that was not brushed and eliminated during the startup, but someone else stated he thought it was scale.

Any suggestions? And thank you in advance for your input!

 

[Bama Rambler]

Post a full set of test results and how you got them. That's the only way we'll be able to guess what it is.

 

[TXFlyGuy]

Test results:
CYA - 86
PH - 7.5
TOT. HARDNESS - 312
MINERALS - 3700
CH - 280
PHOSPHATES - 200
CYA - 60
TA - 120
TAC & FAC - 4
SALINITY - 3300

This is pretty much where we have been except when I did the no drain acid wash. I test the water every other day and usually add acid weekly to keep the PH in balance.

 

[Bama Rambler]

Are those pool store numbers?

Your numbers look good except that your CYA may be a little low but if it's working I wouldn't worry much about it. I doubt it's scaling unless your pH got out of whack for a while.

 

[TXFlyGuy]

OK, if it is not scaling (I never thought it was) what is it? And...how do I fix it to give the pool a nice uniform look? Most of the pool is beautiful, just those few spots. A friend told me I'm the only one who even notices, but it does irritate me!

 

[Bama Rambler]

Other than a complete acid wash you can try a stainless steel bristled brush and lots of elbow grease.

 

[TXFlyGuy]

Other than a complete acid wash you can try a stainless steel bristled brush and lots of elbow grease.

I have used a wire bristle brush and a nylon brush. Is the mottling grayish spotting due to my lack of brushing 5 years ago? So is this leftover plaster dust? Would you suggest another no drain acid wash, i.e., lowering the PH and alkalinity to zero for a few days and brushing like my life depended on it? This is pretty much what I did a couple weeks ago with good, but not perfect results.

Another note of interest...the exposed plaster in between the pebbles is almost black, or perhaps an extremely dark shade of gray. Prior to my de-scaling project the entire pool was a medium milky-gray, kind of like what is left now that I'm trying to scrub away.

Thanks again for your input!

 

[Bama Rambler]

Since the first round worked well I'd suspect a second round concentrating on the bad spots would produce the desired results.

 

[TXFlyGuy]

The first time around 6 gallons of muriatic acid was added to the pool. The total alkalinity was brought down to zero, as was the chlorine, and the PH was around 4 or so, perhaps less. I was advised by some pool pro's to add from 8 to 12 gallons of acid (30,000 gal. pool). Should I have used this amount? If a round two is undertaken should I stick with 6, or go for 8, 10 or 12?

During this procedure the pool pumps were all shut down for the first 3 days.

How long is the acid effective when in the pool water? I noticed after 3 days of brushing (no drain acid wash) that little or no further progress was noticed with regards to removing the light gray areas of mottling. Should more acid have been added at this point?

I'm up for repeating this procedure if you think better results will be achieved. I just went swimming with my mask and studied the entire pool. There is about 20% coverage still remaining of the grayish spots, mostly on the wall directly below the spa dam wall, and and about 4 random patches on the pool floor. These areas are getting brushed vigorously every day now with no visible results observed.

 

[JamesW]

Can you post a picture?

 

[TXFlyGuy]

Can you post a picture?

I would be happy to email some photos...not sure how to post them here.

Can you educate me on the picture posting procedure?

The problem is almost invisible with direct sunlight shining in the pool, but is very noticeable when the sun is at low angles...early morning and late afternoon.

 

[TXFlyGuy]

As you can see, I am not having any luck posting photos!

 

[Richard320]

Can you post a picture?

I would be happy to email some photos...not sure how to post them here.

Can you educate me on the picture posting procedure?

The problem is almost invisible with direct sunlight shining in the pool, but is very noticeable when the sun is at low angles...early morning and late afternoon.

That does sound like scale. I have it, too, a gift from the previous owner.

By scrupulously maintaining CSI in the negatives and working it over with a stainless steel brush, it has been slowly lifting. The blotches are shrinking, and getting bald spots. The easy surfaces - the steps and the spa walls - are almost completely clear of it. This has taken about a year. My big leap forward came after the winter rains last year. I was able to reduce the CH buildup and that seemed to help more than keeping pH and TA low.

I've contemplated doing what you've done, just really blast it with acid, but I'm afraid of etching good plaster rather than dissolving scale. So I stick with the slow method.

If the pictures are big, create a webshots account. If you can't figure out how to direct link, then tell us the screenname you chose and someone will find them. If smaller, use the attachment feature just below the posting window.

 

[TXFlyGuy]

Here are before and after photos...before acid / after acid. The after photo shows how much darker the Tahoe Blue plaster became.

Notice in the entry area in front of the steps the grayish patch...and right at the bottom of each step.

The last picture is to contrast the color before the acid wash was performed.

 

[TXFlyGuy]

These are shown to give a general idea as to what I'm looking for. The tanning ledge is perfect, i.e., no scale issues!

It's difficult to get the problems to show up in pictures, and under direct sunlight they seem to blend in better as to be barely noticeable, except by me, of course!

 

[TXFlyGuy]

[/quote]
By scrupulously maintaining CSI in the negatives and working it over with a stainless steel brush, it has been slowly lifting. The blotches are shrinking, and getting bald spots. The easy surfaces - the steps and the spa walls - are almost completely clear of it. This has taken about a year. My big leap forward came after the winter rains last year. I was able to reduce the CH buildup and that seemed to help more than keeping pH and TA low.

I've contemplated doing what you've done, just really blast it with acid, but I'm afraid of etching good plaster rather than dissolving scale. So I stick with the slow method.
[/quote]

Just read that the no drain acid wash is a very safe way to go, better than draining and then applying acid. Much easier on the plaster also. There are special kits to do this, but plain old muriatic acid is the way to go. Looks like we'll be doing round II in the near future. This time we'll go with 10 gallons of acid rather than 6.