Iron stains keep returning after ascorbic acid
Hi,
I’ve been struggling with a problem with our swimming pool for two years now, and with the start of the new season I’d really like to finally solve it:
Our pool is crystal clear, but it still has a light green coating that’s very hard to remove. It’s not just spots—the entire pool, including the bottom, has a green tint. The only way to get it off the liner is by heavy scraping or scrubbing.
But with a pool that’s 10x5 meters and 2 meters deep, that’s basically impossible to do manually.
After endlessly trying almost everything I could think of, I found out through YouTube that this might be iron staining, and decided to try ascorbic acid. That turned out to be a perfect solution: as soon as I add even a small amount, the staining literally disappears instantly. Last year I added 2 kg at once and within an hour the entire pool was completely blue again.
However, the next problem is that while the iron stains dissolve, as soon as I bring the chlorine level back up, the green staining immediately returns to the liner—so I’m back to square one.
I tried repeating the process and immediately following it with a metal sequestrant, but with the same result: after a few days, everything turned green again.
Now that it’s still relatively cold outside (the water is only 8°C), I don’t need to add chlorine yet, which gives me some extra time to work on this.
My new plan is: add ascorbic acid to remove the stains, then drain about 3/4 of the pool to get rid of most of the dissolved iron. I can’t drain it completely due to groundwater levels and the risk of the liner floating.
Then treat the remaining water with a metal sequestrant and filter thoroughly. After 24 hours, refill the pool with fresh tap water.
Does anyone have experience with this issue, or are there any experts here who have thoughts on this or know about a better approach?
All help and suggestions are greatly appreciated.
Thanks in advance!
