Ring around the collar

[LPCPool]

Hello all. Still relatively new to all of this. 26K Gallon, SWG, in-ground plaster pool.

Starting 3rd season and first year where I'm just having someone help me with opening and closing and I'm taking on the in-between.

Been trying to work on a greenish/yellowish irregular band about 4-5 inches wide that had formed just below the tile line and above the lowered water level from last years closing. I also had some brownish stains on horizontal surfaces like steps and swim outs (that were exposed to air during the off season). Bottom and rest of walls are good. In general, any area that remained above water had some sort of staining issue and anything water covered was fine.

I've been attacking the brown stains with a wire brush and I'm making good headway. But the ring is giving me fits. When I brush it (with the wire brush), it temporarily turns the water cloudy right in the area I'm brushing, but the brushing doesn't necessarily remove the stain. And the clouding disappears right after I stop brushing. So, I'm not sure if I'm just scraping plaster or if I'm actually removing dead algae and that's what's clouding the water.

Overall, the water is crystal, picture perfect clear and, using a DPD kit, it shows no CC (standard 10ml test). FC is holding at around 4/5 (keeping SWG at higher output for now). So, not really sure how to best attack the stains?

 

[frustratedpoolmom]

Determine if they are organic or metal.

In Pool School there is an Index - go to that and find the article about metals and metal stains. A vitamin C tablet will determine metal - an chlorine tablet will determine organic. Once you confirm what they are - then you can formulate a better plan.

 

[LPCPool]

Thank you for the reply and the pointer.

I did the test and it turns out to be metal related. Iron to be specific since the Vitamin C test easily removed any stain it touched.

The follow up question I have is related to where and how the stains came to be:

So, as stated in the first post, the staining occurred in areas that were exposed to air over the winter due to the lowered water level at closing (pool was covered by regular tarp cover - not a safety cover). Areas that were underwater do not have any staining. So, the question is why? What are the mechanics that would come into play for this to happen? Just trying to understand the problem better and hopefully deal with it before it happens next time.

 

[duraleigh]

The source water is the source of the iron content. Is it a well?

Can't tell you exactly why the iron was left behind when the water was lowered. That's not common.

 

[LPCPool]

Water source is city/public water.

Even more puzzling (uncommon?) is that, based on exactly how far the water was lowered, the stain only formed in a narrow band about 4-5" wide right below the tile line. So, not even at what would normally be considered topped off level since that would be at mid tile.

When they lowered the water for last year's closing, they took it down to just below the lowest inlet - about 18" below the tile line - tiles are 4" squares - so, the net level dropped about 20" from the normal in-use level. This meant that the swim outs and all but the lower most steps were exposed to air. The stain band is more greenish/brown while the horizontal surface stains are a more pronounced brown color.

The band of stain starts about 2 inches below the tiles and is irregular and patchy. And is about 4-5" wide at some of the heaviest concentrations. I would've thought that it would've formed in streaks and not just in a narrow band. Or that it would've formed at the lowered water level...not somewhere in between.

If anyone could help me make sense of why/how this happened, I'd really appreciate it.