Freaking OUT! Brown stains on my gunite pool!

[dblomom]

I have an 8 month old gunite pool in Oklahoma. It is 15,000 gallons and is not heated. I have an ozone chlorinator. I am battling brownish stains (similar to what a tea stain looks like) all over the bottom (an some up the sides), they seem to be really bad where the steps are (in that "L" spot that's hard to reach w/ the brush). I read several of the threads here regarding stains and did the Vitamin C test. In less than an hour, I have a humongous BLACK stain where the Vitamin C "sock" was on the bottom of my pool!!! I am FREAKING out b/c this black stain is much larger than the brownish stain was to begin with! My levels are all normal/balanced (chlorine, Ph & total alkalinity). The pool temperature is 78F. Did I mention that I'm freaking out??
I hope someone has a cure-all...
Thanks in advance...

[aylad]

When you say your "levels are all normal/balanced", what do you mean? Can you please post test results (taken with drop-based test, not strips). Also, what is your CYA level?

What is the source of your fill water? Is it known to have metals?

[dblomom]

Janet,

Within in 30 minutes of noticing the big, black stain, it has disappeared! This was a huge blackish-purple stain that was very alarming and is now gone.

I will apologize up front for my ignorance regarding pool chemicals(which may be part of my problem, unfortunately!). Here's what I have:

The total alkalinity: 90
Ph: 7.7
Chlorine:2.0
Temp: 78
CYA:not sure what this is...is this the chlorine level?

Also, the water is very clear!

The pool was filled from my garden hose, which I am on a county water supply. I do not know if it has metals. At this point, I'm leaning towards thinking I have an algae problem because the Vitamin C tab doesn't seem to diminish the stain however, a chlorine tab does seem to lighten the stain. Also, my husband discovered (when we were out working with all of this a little bit ago) that the string that holds the thermometer in the pool is green (it's a white string).

Thanks for your response! I am a pool virgin, but am really trying hard to learn this!

[aylad]

CYA is stabilizer--it wouldn't be in the pool unless you added it, either by adding straight cyanuric acid, or using dichlor powder or trichlor pucks for chlorination. Its purpose is to protect your chlorine from the sun so that it remains in the pool to fight bacteria and viruses in the water. You need to know what your CYA level is, because that's going to determine the amount of chlorine you need to keep in your pool to keep the water clean. (see the best guess chlorine chart link in my sig for more info on this).

You should be able to call the county and ask for lab testing results of the water--they should be able to tell you whether or not it contains metals.

If your white thermometer string is green, then you have algae in the pool. Normally I would say go ahead and shock it, but first you need to know your CYA level and if there are any metals in your water.

[dblomom]

OK, so I visited my Pool company and they checked my CYA for me....they say it's 100.
I have a call in to the county about the metal levels in the water-the Pool company also recommended I do that.
The Pool company is leaning towards iron (especially after the ascorbic "vitamin C" test I did and it turning the spot black and then disappearing) and they have recommended I do the following:
Check the pH and make sure it is b/w 7.0-7.4 and that the chlorine is 1.0 or under. With the pump on, add the "Simplicity" brand Spot Cleaner (after it's been mixed w/ water in a bucket). After an hour, add the "Simplicity" brand Super Metal Control. After another 4-8 hours, add "OMNI" brand Filter Aid. Then, take the filter apart and clean it (b/c I guess the iron is supposed to have been "trapped" in the filter after all of this is said and done).
I hope this sounds right b/c I spent a small fortune at the Pool company service dept. today. :-/

[PoolDoc]

Uh-h. You need to pick who's helping you on this. You'll end up with the worst of both worlds, going from here, to the store, and back to here.

I think maybe you didn't see some of the email replies. I'm going to add them here. I emailed Chem_Geek about what happened and here are his responses:

Nope. Ascorbic acid is acidic and a reducing agent. The brown turning black sound more like oxidation. I noticed you asked her for the brand — maybe there was something else in the Vitamin C tablet. Either that or maybe the ascorbic acid reduced iron but then there was extra chlorine that re-oxidized it black. Since the ascorbic acid was in a sock, that sounds most logical since it probably wasn’t enough to remove all the chlorine in the pool.

and

Normally, stains don’t reappear after even a local ascorbic acid treatment, but maybe this particular pool has a LOT of iron in it. Probably doing your technique of trying to capture the iron in the filter by raising the pH through the skimmer would work — assuming the filter is a sand filter that could be readily backwashed.

After he sent me those comments, I got your email about the black spot going away AND about the Vitamin C clearing the spot around the tablet. That made things fairly clear: you have iron stains. The vitamin C in a sock reduced the stains, in place, to a black "ferrous" iron state, but that gradually disappeared because ferrous iron soluble. The more direct application of vitamin C behaved in a more typical fashion.

If you're going to follow their program, that's fine. It sound similar to what I would have done, but I'm not sure because I'm just guessing at what the chemicals are. Also, the program they've got you on is likely to allow algae to grow, while you work on iron, and I'm not sure if that's what you want to do.

Regardless, do lower the pH. But, if you lower the chlorine to 1.0 with a CYA of 100 . . . your algae is going to take over, and the pool store should have known that and warned you.

Your choice though.