Mysterious stain after opening my pool

[shoot_the_goalie]

Wondering if anyone could possibly help me to identify a stain. Opened the pool about a week ago (closed in mid Oct at good water chemistry and no issues with pool). At opening, typical debris in pool, but water was clear. Noticed a large stain around one of the spa returns that looked like a rust stain (pic 1).


Took a metal brush and a lot of elbow grease and got a lot of the stain removed (without any chemicals) except the dark "teardrop" spot (pic 2).


24 hours later, small parts of the stain re-appeared as a light orange color, which then turns to reddish-orange (pic 3 as well as other pics taken underwater).



Took a vitamin C tablet to the stain, but nothing really happened; stain didn't lighten much. Then took a tri-chlor tablet to the stain, and still not much. The only thing that seems to remove the stain is vigorous brushing with a metal brush, but again, that only removes the reddish-brown part of the stain. Checked inside the return (which was plugged over the winter), and no signs of rust, objects, organic material, or any stain inside the PVC housing, so the stain seems to be emanating from where the PVC flange connects with the Hydrazzo plaster. Pool is in it's 4th season, and plaster looks pretty good, except for this spot.

Thoughts?

 

[JamesW]

Probably steel rebar or wire ties beneath the plaster.

Try a magnet to see if it sticks in the area.

 

[shoot_the_goalie]

Just tried your suggestion...magnet does not stick to any areas.

 

[JamesW]

Did you use a really strong magnet?

 

[shoot_the_goalie]

Did you use a really strong magnet?

I was able to procure a neodymium magnet with a max pull force of 75lbs (way stronger than the one I initially used). I put it around the area and it does not "stick". I don't feel any sort of magnetic attraction at all. Would that mean this is probably an organic stain then? (I put a little tri-chlor on it and it didn't do much, but I didn't really scrub).

If it helps any, the new formation of the stain is first a light orange color (like pic 3), and is more prevalent in the am hours. Then by the afternoon it turns to a dark orange/brown. Then it cycles again the next day; light orange in the am and so on....

On a side note, if it were indeed a rebar/rebar tie problem, is that something you would need to repair immediately, or would it be something ok to put off a few months until closing? I'd imagine rebar would take quite a long time to corrode completely where it would be a harm to the pool structure?

 

[JamesW]

I'm pretty sure that it's steel.

It's mostly cosmetic. It can't really affect the structural integrity in any significant way.

You're going to have to cut out the bad section and patch to fix it.

It will spread. So, the longer you wait, the worse it will get.

Put the magnet near the orange and scrape some off to see if the orange floats to the magnet.

 

[shoot_the_goalie]

My PB (reputable co.) is gonna take a look at it and see what they can do.

Glad to hear that it's mostly a cosmetic issue. Was a little worried something was corroding away and would cause a bigger issue.

Appreciate all the help James.

 

[shoot_the_goalie]

Added note: I scrapped away some of the light orange growth, and it flaked away. Had my 75lb magnet and the orange flakes did not attract to the magnet.

 

[JamesW]

The only thing that I can think that it would be is iron, but the tests don't seem to support that.

I think that you're going to have to cut into the plaster and see what's going on underneath.

 

[Rich D]

Perhaps you had some winter freeze damage to the return itself and this is either groundwater coming in or water from the cracked return pushing through the opening in the gunite for the return. Does the reformation of the stain differ if you shut off that return so it is no longer in use?

 

[shoot_the_goalie]

Perhaps you had some winter freeze damage to the return itself and this is either groundwater coming in or water from the cracked return pushing through the opening in the gunite for the return. Does the reformation of the stain differ if you shut off that return so it is no longer in use?

Do you mean to suggest there's a crack in the shell and/or return and ground water is coming through? As far as I know, there is no signs of leak (water loss) in the pool besides normal evaporation. Also, right behind the return, I believe the gunite is like 6" thick. The water table here is very low here and the pool is embedded in very compacted soil and bedrock. I also checked the inside of the return, and it all looks fine...no signs of anything abnormal. Pool operation is all normal.

The stain itself forms consistently, no matter if the return is on or off. Most of the time, that return is only on a tiny amount, as I have the spa return valves almost closed unless using the spa.

 

[shoot_the_goalie]

I'm pretty sure that it's steel.

It's mostly cosmetic. It can't really affect the structural integrity in any significant way.

You're going to have to cut out the bad section and patch to fix it.

It will spread. So, the longer you wait, the worse it will get.

Put the magnet near the orange and scrape some off to see if the orange floats to the magnet.

It's been taking a bit of time to get my PB to take a look at this, understandably due to the current COVID situation, so I had a few questions in the meantime. If this is indeed rust (which I think it is), since it's releasing a little bit of rust particles every day, is it a danger in any way? I keep my water chem levels pretty on point (water is crystal clear), and it's not a ton of rust particles released every day (from the small light orange bubbles that form). As you previously stated, it's not a danger to the structure of the pool, but would this cause my iron levels in my pool to go up, and would that be bad for people swimming in the pool? Could it cause staining in other parts of the pool? Or would it just get filtered out my the filter cartridges and not really affect the iron levels? Thanks.