Plaster & Plastic Parts discoloration

[DGL]

Hi, over the course of the past 3 years our pool plaster developed some brownish discolorations, predominantly on the vertical parts, pictures attached.

Also the plastic return nozzles started turning brown. It does not look like a deposit, but a discoloration of the plaster itself. It cannot be brushed off and I tried ascorbic acid without success. Not sure how old the plaster is, as we bought the house just 3 years ago, but I would assume 5-8 years.

Pool chemistry: Typically we have FC 2-4 with CYA 30-40. pH has not always been immediately addressed when turning high. so we had longer periods with 7.8-8.2, but try to maintain 7.5-7.8 TA was typically at the low end with 70-80, CH as well with 180-210. We did not bother too much about phosphates in the past and stopped dosing Anti-Phos, so this went up to about 1,000.

Any ideas / suggestions are welcome.
Thanks,
Dennis

 

[kadavis]

Plastic has an affinity for iron.You might want to have your water checked for metals. It almost looks like all the staining is right below your rocks, any chance it could be bleeding something into the water

 

[pooldv]

Rub some Vit C tabs on the stains and see if it lifts the stain. We have other members with rocks that leach iron into the water. Are you on city water?

More here, Pool School - Metals in the Water and Metal Stains

 

[JamesW]

Definitely looks like iron, but the ascorbic acid should have had some effect.

Maybe something from the rocks in the waterfall. Are they natural rocks or artificial? Has the color of the rocks been enhanced somehow with a stain treatment?

 

[Swampwoman]

What kind of rocks are those and do you ever periodically seal them? I would be highly suspicious that they're leeching.
Alternately, are you on well?

Iron can also combine with both calcium and phosphate to form scale that is difficult to remove. For this reason, try dry acid on it, then vit c after the dry acid in a test spot, and see if it doesn't lighten.

If it does, you way wish to do an "underwater acid wash" with a tool like this one: Amazon.com: Purity Pool UAW Underwater Acid Wash Set: Patio, Lawn Garden

 

[DGL]

Thanks for all the comments.
I had the water tested for iron and copper and results came back as 0.
Ascobric Acid / Vitamin C rub did not brighten the spots.
We are on municipal water supply, quality is good.
The rocks are natural, but very soft, like lava rock. They are not sealed. Every two years I pressure wash them which carries a lot of material into the pool which I then vacuum. As the color of the rocks does not really change after pressure washing I do not believe they are stained.
We have these stains also in other parts where there are no rocks above and the pool store said it would be normal aging of the plaster.
I thought of bringing CH up a bit, maybe calcium is leaching out of the plaster, causing the discoloration.

 

[JamesW]

Probably something from the rocks. It might be iron. Do you know about the rocks? Type, source, composition etc?