Stain (non-organic) on deep side of pool floor

[giant_donut]

I have noticed this stain for a while and originally thought it was Algae. After shocking, placing a chlorine puck on it, and trying to put Vitamin C on it, I was not able to lessen the stain. Since it is on the deep end it is very had to scrub Vitamin C on it (thinking it might be an Iron stain). I crushed Vitamin C tablets in a filter sock and placed it on top of the stain as well but did not notice it go down. At this point I was thinking of using the Ascorbic Acid treatment but I wanted to confirm if this is the right step.

Edited to add: I went to Leslie's to test for Copper/Iron and they found none. I use the Taylor kit to test.

(I no longer use the salt generator as the Hayward Aqualogic Circuit Board failed and have not gotten around to repairing it)

FC 3.0 (LC)
CC 0.5
PH 7.4
TA 50
CH 550
CYA 40
Salt 2400

 

[Texas Splash]

Since a puck and vitamin c did nothing, you might try some dry acid in a sock or nylon as well. Even though Leslie's didn't show any metals, let's see if there is any reaction. If that doesn't work, we may have to get more creative in our evaluations.

 

[JamesW]

Something in the water won't create a spot stain.

Probably an iron stain from rebar in the gunite sticking up..

See if a strong magnet sticks to the spot.

 

[giant_donut]

Since a puck and vitamin c did nothing, you might try some dry acid in a sock or nylon as well. Even though Leslie's didn't show any metals, let's see if there is any reaction. If that doesn't work, we may have to get more creative in our evaluations.

Does dry acid here mean ascorbic acid or a different type?

 

[PoolStored]

Does dry acid here mean ascorbic acid or a different type?

Dry Acid = Sodium Bisulfate. Search Google for "dry acid pool."

 

[giant_donut]

Dry Acid = Sodium Bisulfate. Search Google for "dry acid pool."

Since a puck and vitamin c did nothing, you might try some dry acid in a sock or nylon as well. Even though Leslie's didn't show any metals, let's see if there is any reaction. If that doesn't work, we may have to get more creative in our evaluations.

I did two applications of Dry Acid in a nylon sock over the stain. After srubbing it a bit with a brush it started to peel away! It’s still lightly visible but I’ll apply another set of the Dry Acid in another day or two. Thanks so much for the recommendation!

 

[giant_donut]

Hi All! It seems the stain came back after applying dry acid directly to the location. Not only that but I have this new stain that may have resulted from it. I noticed my FC dropped low so I added 1 gallon of LC (10%). Waiting to see if adding LC helps.

Any thoughts? Should I try Dry Acid again or use Ascorbic Acid? SLAM the pool? Latest pool readings in the PoolMath.

 

[Texas Splash]

Should I try Dry Acid again or use Ascorbic Acid? SLAM the pool? Latest pool readings in the PoolMath.

Before you try anything else I would recommend an Overnight Chlorine Loss Test. Let's be sure there is no algae issues first. If you pass the OCLT, then you can test once again as follows:
- Vitamin C - iron
- Dry Acid - copper

 

[giant_donut]

Before you try anything else I would recommend an Overnight Chlorine Loss Test. Let's be sure there is no algae issues first. If you pass the OCLT, then you can test once again as follows:
- Vitamin C - iron
- Dry Acid - copper

Will do! Just added another gallon and will record the reading once the sun goes down and first thing in the morning.

 

[giant_donut]

Before you try anything else I would recommend an Overnight Chlorine Loss Test. Let's be sure there is no algae issues first. If you pass the OCLT, then you can test once again as follows:
- Vitamin C - iron
- Dry Acid - copper

No significant loss in chlorine.
FC (yesterday evening) = 5.5ppm
FC (this morning) = 5.0ppm

Loss of 0.5ppm. Based on my readings this passes OCLT.

 

[Texas Splash]

Loss of 0.5ppm. Based on my readings this passes OCLT.

That would seem to rule out algae. A bit of an odd situation since in the beginning you tried Vitamin C with no positive result, but that spot sure seems to be indicative of something showing up from underneath like JamesW noted. You might try the Vitamin C again, or maybe see if a strong magnet will to attach itself to that area which might confirm the presence of rebar close to the surface. To make things more odd, the dry acid did seem to work for you which would point to copper. By any chance have you pulled your cartridges out of the filter recently? If you do have excess copper in the water, those paper carts could show signs of discoloration.

 

[giant_donut]

That would seem to rule out algae. A bit of an odd situation since in the beginning you tried Vitamin C with no positive result, but that spot sure seems to be indicative of something showing up from underneath like JamesW noted. You might try the Vitamin C again, or maybe see if a strong magnet will to attach itself to that area which might confirm the presence of rebar close to the surface. To make things more odd, the dry acid did seem to work for you which would point to copper. By any chance have you pulled your cartridges out of the filter recently? If you do have excess copper in the water, those paper carts could show signs of discoloration.

I purchased ascorbic acid so I can put them in a nylon sock and try again. Also on dry acid, is there any risk of damaging the plaster by placing dry acid directly on the stain spot? The stain doesn’t exactly brush away, I have to use the end of the pole to “scrape” it off.
I’ll also try a strong magnet to check the presence of rebar.
I haven’t pulled out the cartridges recently, only opened it during the last ice storm to add water after draining it. It is definitely time for a cleaning but didn’t look too discolored.

 

[Texas Splash]

is there any risk of damaging the plaster by placing dry acid directly on the stain spot? The stain doesn’t exactly brush away, I have to use the end of the pole to “scrape” it off.

I wouldn't leave it there in one place for too long. Rub it around just like anything else. If it is going to work you should tell rather quickly. There should be no need to scrape with anything sharp, so I would avoid that so you don't damage the plaster surface.

 

[JamesW]

The only way that it is going to come back in the same spot is if it is rebar.

The blue and black looks like copper.

 

[giant_donut]

The magnet did not seem to stick to that specific area. It probably is rebar if the stain keeps appearing.

I’ll try another application of dry acid unless it is stated otherwise.

 

[JamesW]

Was it a strong magnet?

 

[giant_donut]

Not really, just the strongest I have that is on the fridge :/

 

[JamesW]

It's probably rebar and it also looks like copper stains in general.

I suspect that the rebar will continue to reappear until it gets fixed.

Copper can be cleared by sulfamic acid in many cases, but then you need to drain and refill if it is safe to do so.