Mystery stains on liner

[Skeeter]

Hi all, I'm stumped on this one. So this little patch of yellow/brown stain appeared towards the end of last season. Can't brush it off, looks like a stain but thought it might be organic so I SLAMmed. I worked hard to keep FC greater than 30 ppm for a few weeks but the stain remained, and it was still there when I closed the pool. This year when I opened, the water itself was pretty clear and was crystal clear in a day after opening. I noticed that the stain had now "spread" and is covering alot of the liner now. I broke down and used "Yellow Out" and followed the instructions to the letter. Since then, I've been at SLAM levels for a week (FC= 30+, CYA= 40-50) and the FC remains within 1.5 ppm of the previous night's reading the next morning. CC is <0.5ppm. I use liquid pool chlorine from Walmart (Bleach) and powdered cal-hypo "shock" packs. It almost looks to me like the stains are getting worse the more I chlorinate, is this possible? pH was 7.8 when I treated with Yellow-Out, and is now 7.2-7.4. Alk is 90, CH is 220-240. I bought 2 trichlor tablets and have them sitting directly on the stain for 36 hours now; no change except for a slight white ring (think drink ring) under where one was sitting. Stain will not brush off. Any ideas? Pics are attached, the stain looks darker in the pics than it actually is (it's more yellow-brown than brown)Thanks!!


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[Texas Splash]

Don't use the tabs anymore like that. The tab test should only be for a few minutes and not sitting for so long. You may have permanent drink rings there now. Try some crushed vitamin C tabs in a thin sock or nylon. If that works, it's iron. Let us know.

 

[Skeeter]

Don't use the tabs anymore like that. The tab test should only be for a few minutes and not sitting for so long. You may have permanent drink rings there now. Try some crushed vitamin C tabs in a thin sock or nylon. If that works, it's iron. Let us know.

Thanks! I wasn't sure how long I needed to leave the tab there to see if it's organic, I'll pull them out ASAP. I'm due for a liner (probably next season, though I said that last year too!) so I won't beat myself up too bad over the drink ring. I'll try the vitamin C and report back. Any recommendation on a brand of Vitamin C? How long should I keep it there before I should expect to see a result?

On a side note, I just re-read my first posts from back in 2014. Other than this stain, I can't believe the difference in my pool routine between then and now... I've been a TFP convert for 5 years and haven't looked back, thanks for the advice back then to set me straight!

 

[Texas Splash]

Any recommendation on a brand of Vitamin C? How long should I keep it there before I should expect to see a result?

The brand shouldn't matter really. You should see a difference in a short amount of time if it's iron. Maybe a couple minutes, but you can leave it for 5-10 if needed.

 

[Skeeter]

Great call on the Vitamin C. I picked up some chewable tablets, crushed them up into cheesecloth, then dropped it onto one of the spots. Sure enough, the liner under it completely cleared up within seconds. Searching the forum turned up a great looking write up on Iron, looks like I’ll be grabbing some ascorbic acid.

I find it ironic (no pun intended) that the treatment I was doing for the “algae” was the one thing that will make iron problems worse!

Thanks for the help!