Mystery Stain - Brownish Color

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Andrea Goldsmith

Member
Jun 20, 2019
9
Sacramento, CA
About a week ago a stain developed in my pool (it developed over a two day period). The stain is on the bottom of the plaster pool and as you can see it looks like there is an origin point and moves towards the return. I tried to brush it with a wire brush, but it didn't budge. My pool is 12 years old and I have never had problems with stains (we are on city water). My water is balanced and crystal clear. I don't think it is an algae because I performed the overnight FC test and lost less than .5. I thought that something metal/rock dropped in my pool, but I searched the filters and did not find out foreign matter. Over the last week it seems to b e getting darker but not spreading. There are no signs of any other stains. Is it possible that I have a small hole at the origin? I turned off the auto fill and my pool dropped about 1" in 4 days. I live in Sacramento and it has been between 89-104 degrees during that period of time. I did not know how much water loss is considered normal. I wanted to find the root cause of the problem before trying to remove the stain. How should I go about determine the root cause of this issue?

PH: 7.8
TA: 100
CC: Try to keep it around 4-5
CYA: 30
CH 275

108181
 
Could be an exposed piece of rebar. Although I would not think the stain would get that dark that quickly.

I would put a vitamin c tablet on it and see if it fades or disappears. That would confirm iron staining.
 
When you refer to vitamin C tablet, are you referring to the ones you can get in the health store or are there tablets made for pools (if so, what brand do you recommend)? The stain is on the bottom of our pool (our pool is about 5ft deep). Should I put it in a sock and hold it in place with a pool brush? How long do I need to keep the vitamin C on the stain?
 
Yes just the tablets you would eat. It should have an impact within a few minutes. Try 1 and see what happens.

If the stain goes away, you could crush up a bunch in a sock and set it on the stain and move it around until the stain is gone.

You might want to then get down there with goggles and inspect where the stain started to see if anything is visible.
 
Well the verdict is in. It is definitely an iron stain. Within a minute or two of applying the Vit C the stain decreased. It is about 3/4 gone, so I will need to work on it some more. I showed the picture to the pool builder and he said it was probably a metal tie (I am surprised it took 12 years to showup). On an ongoing basis, I am going to keep my ph at 7.2 and add sequestering agent (I have not used it in the past) in hopes of keeping the stain abay. In addition to the stain, there is a lot of calcium buildup on the tile at the waterline & the wall with the waterfall (present when I purchased the house), which makes me fear that there is calcium buildup on the pool equipment. Would you recommend that I follow this procedure for removing the rest of the stain Ascorbic Treatment to rid Pool of metal stains I thought it might help the equipment (I know it won't improve the calcium build-up on the walls - I am going to have it professionally blasted).
 
I don't think the AA is needed. The stain is completely localized, right. I also am not sure the sequestrant is going to help. That is to prevent metal in the water from depositing on the pool surface and this did not likely put enough metal in the water to risk staining everywhere. Your stain is likely due to a piece of metal exposed. The stain will keep coming back until the exposed metal is removed or covered.
 
I thought an iron stain that is due to construction of a pool would show up in the first couple of years. This pool is 12 years old. Is it because the plaster is getting thinner? How is this type of issue fixed? Does it need to be re-plastered? What is the likelihood that it will still be a problem after re-plastering?
 
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