Yellow (orange?) discoloration on horizontal and verticle surfaces

tpribors

Member
Aug 2, 2019
21
Las Vegas, NV
About 6-8 weeks ago I noticed some yellow or orange discoloration starting to appear. At that time it was mostly it was on the bottom surface and on the steps of the spa. At first it was some splotches in the deep. It’s not rebar rust – this is too wide spread and splotchy (and I've seen rebar rust and this ain't it :) ). I don’t know if the right term is “staining” but it’s become pretty wide spread now… At first it was on horizontal surfaces but in the past few weeks has appeared on vertical surfaces too.

I don’t believe it is organic. At first I thought the splotches were algae and I shocked the pool. It can’t be brushed away, and also resists scrubbing with the scrubbing pads, sandpaper and even scraping with a paint scraper. Sandpaper did get it off in a small test patch but it wasn’t easy and I could see plaster raising before the stain did. Also there is a spot on the seat in the spa so I drained the water down below the seat and tried acid and bleach on it, no effect.

stain 1.JPGstain 2.JPG
 

tpribors

Member
Aug 2, 2019
21
Las Vegas, NV
What would be an iron source that is this widespread? Our water (Vegas) is off the charts for calcium from the tap, but it doesn't have any iron hardness. The only source I can think of is the rebar, but I've seen rebar stains (a friend's pool) and they are much more localized and very dark and come from the "back". This appears to be a surface deposit.

I've thought about a dose of "Vitamin C" but what quantity would I use for a 21000 gallon pool, and is the proper bulk chemical ascorbic acid or acetic acid? Does it have any side effects, e.g., interaction with ph, chlorine, CYA etc? (Also, this is a salt water pool, so is it safe to leave the generator in place, and operational or disabled?)
 
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