First pool, solving stain issue

[mattdf23]

I hope this is the right place for this question. I have a now 1-year old pool, and am still learning the ins and outs of pool maintenance. I do regularly test with the TF-100 test kit, and try to keep the chemistry as balanced as possible.

Over the past few months I have noticed some spotted staining on the plaster. It looks to me like a rust or metallic looking color, and it primarily stains (or shows) on the mother of pearl shells that were cast throughout the pool during the plaster stage to provide a shimmer.

The stains will brush away, but require a fairly thorough brushing. Regular weekly brushing by my pool crew does nothing, it requires several passes to clear up. The stains will re-appear over the course of 1-2 weeks.

I've included some pictures to hopefully provide additional information. The first picture is before brushing, the second after brushing. I'm not sure if this is rust staining, some other metal staining, some type of algae, or what.

I will say I have identified a "rust colored" spot about the size of a nail head just above one of my benches. This spot will not brush away, so I'm afraid its possibly a rebar tie protruding through the plaster? (Third Picture)

I would love some advice as to how to narrow this down, and possibly address with the pool builder. Thanks!

Before Brushing


After Brushing


Rust Spot above Bench

 

[Texas Splash]

Matt, a lot can happen in one year, so it's probably best we start with a full set of test results from your TF-100. As for the bench, you can rub a vitamin C tab on it. If it goes away, you know it's iron. You can try that with any other areas you wish as well. If they don't go away, my guess is they are organic which can be tested by rubbing gently or placing a chlorine tab on an area for a short bit. If any of those areas get worse with a test, let us know.

Have you added anything else to the water other than than norm (salt, acid, etc)? Even though you're in Houston, some areas have reported excessive iron in their supply. Do you know of such levels in your area?

 

[mattdf23]

Thanks for your response. I have not added anything besides the basic chemicals: salt, acid, CYA. I tested my water tonight, the results are below. I plan to add a bit of CYA this weekend. I believe the heavy rains we've experienced here in Houston have washed some out.

PH: 7.2
Chlorine: 4.0
CH: 275
TA: 60
CYA: 40
Salt: 3000 ppm
Temp: 89 F

I will try to test the spotted stains tomorrow with both chlorine and vitamin C tabs. I appreciate the suggestion.

As for the fill water, I honestly do not have any information regarding the iron levels in the local city water.

 

[skimmerswimmer]

Bump up your FC by a few ppm for a week or two and see if the stuff that requires hard brushing goes away.

 

[mattdf23]

So a quick update. I tested today with Vitamin C. By just placing a tab on a spot it definitely seemed to remove the stain.

After thoroughly rubbing the "rust spot above the bench" pictured above with a Vitamin C tab, the surrounding staining was removed, but the primary black spot remained. I'm still thinking this could be the source of the metal contamination (rebar tie or something).

Any recommendations on next steps? I still need to identify the source obviously, but the staining seems to be getting worse. As I battle with the pool builder over what the spot over the bench is, I would at least like to try to slow/remove the spotted staining throughout the rest of the pool.

 

[Texas Splash]

So Vitamin C removed one stain, but did nothing for the other right? So the other staining must be organic, copper, or something else we may need additional advice for to see if there is an issue with the material itself. To rule-out organic, try gently rubbing a chlorine tab on the area. If it lightens, it's organic and you need to increase the FC level for a while with lots of brushing. If the tab makes the stain worse, it's probably copper. At that point you can place some dry acid on the area to see if it lightens to confirm.

If neither of those work, we'll need to expand our areas of consideration to see what it could be.