Discolorations on plaster

Mcb

Well-known member
Jan 3, 2018
71
Chino hills, CA
I'm trying to figure out what is going on here. We had the plaster acid washed when we moved in to get rid of. Black algae. We had other repairs made including a rusty piece of rebar. It appears near the drain I'm getting black spots. Some are linear which makes me wonder if that is more rebar issues. The side walls have a yellow/grey type tint. You can see it is up and down like where the acid was poured and scrubbed. My neighbor gave me dry acid and told me to let it sink to the bottom in a sock to help get rid of it it. I havent had a chance to try it yet. This weekend.

My levels are always with in acceptable range. I keep the PH on the low end around 7.2 as it is always rising. FC I aim for 10 and dose 10% bleach and MA daily 8oz of each to keep everything in check.

Im not sure now to investigate or fix this.

Thoughts?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,446
Laughlin, NV
How do your test your water chemistry? Do you have a full set of test results?

Acid wash does not eliminate algae. But, I would suspect that it would erode plaster that is older such that more rebar may show through.

I would delay on the powdered acid test. We recommend using a chlorine tablet to test for organics. Is that what you were doing? Acid is not used to test for removing a stain from anything.

Take care.
 

Mcb

Well-known member
Jan 3, 2018
71
Chino hills, CA
I have the k2006 test kit.

I'm not familiar with the tab testing.

Neighbor said the spot should go away in 12 hours. Not really sure what it reacts with.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,446
Laughlin, NV
Thank you on the test results. Look good to me.

I would never place dry acid in one spot on a plaster pool for any amount of time. I would stress please do not do that.

What are you trying to remove or test for?
 

Mcb

Well-known member
Jan 3, 2018
71
Chino hills, CA
Thank you on the test results. Look good to me.

I would never place dry acid in one spot on a plaster pool for any amount of time. I would stress please do not do that.

What are you trying to remove or test for?
I'm not sure where to start with the black dots forming on the bottom on the bottom. I'm not sure how to start troubleshooting.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,446
Laughlin, NV
You mentioned black algae before. Was it in that area too? Black algae has a specific process to remove, see Pool School - Black Algae. It can be problematic to eliminate as the roots can get deep into plaster, especially older plaster that has been eroded due to maintaining water with parameters with a CSI of below -0.6.

Do you monitor CSI? Your test results above are in the OK range but with any lower pH you would have aggressive water chemistry.

If they are iron stains from rebar, you will not remove them. They will be reoccurring and it is time to recondition the pool surface.
 

Mcb

Well-known member
Jan 3, 2018
71
Chino hills, CA
What is CSI? I'll read up on the black algae removal. You would think that the acid wash would have done it. It was completed the first week in January. Would it start to resurface already it the chlorine was maintained correctly. What else would cause the black spots? What about the weird yellow brown wavy discolorations
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,446
Laughlin, NV
Chlorine is needed for algae removal.

Black algae can be chlorine resistant. Read the Pool School article. Your FC you listed is not all that high based on [FC/CYA][/FC/CYA].

The discolorations do not show on the pictures. The colors you state could imply algae. Have you done an Overnight Chlorine Loss Test lately?

How do you chlorinate?

Take care.

- - - Updated - - -

CSI -- Calcite Saturation Index - requires pH, TA, CH, CYA, Temp, uses Borate, Salt
Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools.
Greater than 0.6 is suggestive of problems for all pools.
 

Mcb

Well-known member
Jan 3, 2018
71
Chino hills, CA
I use liquid, 10%.

Once it dips to 8 I dose it back to 10, which I believe is the upper range?

I read the article. It references acid can discolor plaster. Wonder it that is the cause. I scrub the side walls pretty hard I would think it would knock algae off, but im pretty new to this. I did hurt my back 3 weeks ago and have not scrubbed like I had before. I'm wondering if that is the cause. Finally back on the mend and can get going again. I think that's why I noticed this.

I'll do the OLCT. Never done it before, but read about it. Also I'll research the CSI test procedure.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,446
Laughlin, NV
It is shown on the app. It is automatically calculated as long as you have data for it. Look at your Logs. It is the last item in each log.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
11,643
Evans, Georgia
I'd try using PoolMath on the computer if you're having trouble seeing it on the mobile device.

We avoid the use of dry acid as its not good for plaster nor salt water chlorine generators. MA is much better for dropping pH. Using straight MA on stains can be iffy as you might cause a change in the plaster too.

Maddie :flower: