Rust stains... Taking advantage of closing to get rid of the iron

[superdave5599]

I've got what I believe are rust stains in the pool. Last year, there was some noticeable around the skimmer housing, but that was about it and I didn't really worry about it. This year, I put a protective mat under the removable steps and seat I installed, and when I pull them up to clean, there is slight orangish staining evident next to where I can see the bright blue liner where the mat was. I also noted some rust spots on the vacuum skimmer cover (it is in place most of the time, as it runs a suction cleaner most of the time.)

Took a sample of water to the pool store (I'm pretty sure I've seen that this one test can be OK there... ha ha) I was told that the iron is 0.1 (ppm I suppose) I don't remember the copper number (forgot to write it down), but it was trace. For reference, I took a sample of fill water from the kitchen sink and it was at copper 0.7 and iron 0.2. I suppose all the rain we've gotten this summer probably accounts for pool being slightly lower for both.

Could it be something else?

I have just now seen recommendations of vitamin C in a sock-- is it really just dumping vitamin C supplement tablets in a sock and trying to rub the stain off? I tried one tablet a few weeks ago, but it appeared that might have actually been scratching the pattern on the liner so I quit.

 

[reggiehammond]

Once the metal precipitates to create the stain, it's no longer in the water to where the rather inaccurate metal testing can pick it up.
Can you post some photos of the area? Vit C tabs should be crushed into a powder inside the sock...

Stains in Your Pool

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[superdave5599]

Ok, well it is a couple months later... Lot of family stuff that has happened in the interim, that really prevented me from being able to worry about anything pool-wise, beyond making sure the chlorinator was running and I didn't have any algae. Though I did noodle on this a little a couple times here and there.

Now, it is about closing time, and I want to see if what I'm thinking is correct.

From reading the stain article back in August, along with other threads, it was my impression that once you start using sequestrant, you are pretty much stuck with having to stay on top of that, too. I wasn't super excited about that if it can be avoided.

If I use the Ascorbic Acid treatment, do I understand correctly that it will lift the stains, and keep them in suspension as long as the PH is low and there is no chlorine? And the sequestrant is simply to keep the stain/iron in solution once the Ascorbic Acid has been neutralized?

If that is close to true, then what I'm thinking is maybe I can drop the chlorine (my ignoring it combined with low temps and less sun means that at today's test it is 16 ppm, oops!), then dose it with the ascorbic acid to lift the stains, then just dump that water out, along with the iron that is carried by the acid, when closing the pool. Maybe lower the water a little bit more than I otherwise would need to. Then, when I fill it in the spring, it'll be diluted enough that perhaps I won't have to worry about the sequestrant.

[I think at least one big source of the iron was an anti-kink spring that was on the garden hose I'd used to pump water through my kludgy solar heater. That spring rusted and was under the water surface for quite a while.]

I can dose the remaining water with bleach for the winter SLAM level, and use a sump pump to mix it around, along with any PH adjusting stuff that may be needed.

Does this seem like a decent plan given that I could close the pool at any point now? Am I correct on my thought on not needing sequestrant at this point, since the plan is to dump the water before re-adding chlorine and adjusting PH?

Pics are from this afternoon after sweeping up some dust that had accumulated. I had mats under a bench and steps, and the stains are most noticeable where you can see the edge of the mat. The phone camera didn't capture the yellowish color of the liner very well compared to the blue under where the mats were, but you can see the line.

 

[superdave5599]

I resurrected an old thread I started in the summer, but it's in The Deep End and I don't think it is getting much traction over there.

Anyway, I have what I believe is some iron/rust staining on my liner, and the skimmer. I think it came from the anti-kink spring that was on a garden hose I'd used to send water through my homemade heaters, as the fill water tested low.

Also, the water is now under 60 so I could close at any time. And, it is a little high from a bunch of rain we had over the past couple weeks.

I know that typically when using something like Ascorbic Acid to lift stains, the metal is still suspended in the water, and needs a sequestrant level maintained to keep it suspended.

What I'm thinking I could try is, drop the chlorine to zero or nearly over the next few days, then do the acid treatment on say Friday, and then once the stains are gone, immediately lower the water level to the winter level, carrying a good percentage of the metal-laden water with it. Perhaps even lower it a little more than I typically would need to for winter.

Then, I can raise the chlorine level in the remaining water back to SLAM level (using a sump pump and hose to circulate it around, or maybe pumping from main drain only and letting it splash out the returns) and proceed with regular closing from there.

Thought is, I may be able to reduce the metal in the water enough that it'll be diluted enough when I refill the pool, that the stains won't reappear, and I won't need to use the sequestrant. And if that doesn't work, then I'm still using sequestrant next year, and am mostly out the time and money for the ascorbic acid.

Right??

Couple follow ups:

Could adding the chlorine to the remaining water at the end of this process cause whatever iron to re-stain the bottom of the pool? Would switching to polyquat be a better bet for this winter if I'm going to give this a shot? Or, I guess if it did stain, I could do another acid treatment on the lower water level, and hope that the dilution idea still works, right? (Only real reason I'd prefer to use chlorine for closing is I have several bottles sitting in the basement unused...)

Whether I use chlorine or polyquat, do I really need to worry about things like PH for the over-winter water? Only thing it'll be touching is the liner I suppose, so is that OK if it is low? Or should I worry about getting that back up?

If I'm hoping for a big dilution in the spring, how low is considered safe for the liner? About a foot of water in the shallow end, right?

 

[ajw22]

Low pH causes wrinkles in liners.

Much of what you read about stain treatments is aimed at plaster pools that can take a lot more abuse then your liner.

I would be careful about being too aggressive in treating stains in your liner. The stains are only cosmetic but the effects of the stain treatments can damage the liner.

Sequestrant is unlikely to last through the winter and there is a good chance the stains you remove right before closing will redeposit on the surfaces. I would wait until you open the pool int he Spring to do any stain treatments.

 

[superdave5599]

Thanks for that info on PH, if I choose to go this route, I will be sure to not ignore that when I'm all done!

Though my whole goal is to hopefully get the iron out by getting it in suspension with the ascorbic acid, and then immediately dumping it to hopefully not need any sequestrant at all, now or in the future. I'm pretty sure I know where it came from (that rusty spring) and the fill water is low iron per (pool store...) testing, so hopefully when I refill and therefore dilute the remaining water, I won't need sequestrant at all.

 

[superdave5599]

Sorry to everyone for the repeat info/questions in this thread... I started a different one in the opening/closing forum because I felt my plan to take advantage of closing to dump the water out was more relevant there than over here, and there seem(ed) to be less activity in this forum this time of year. But a mod moved that post to this thread. So here we are.

 

[superdave5599]

I had some vitamin C tablets, so I crushed them up, strapped to the brush, and was surprised at how readily it took up the staining. And pleasantly surprised that the cleaned liner didn't look as faded as I had thought!

I think I'm going to proceed as described above, unless someone can tell me a reason it is a bad idea. Probably this weekend.

Would still like any thoughts about chlorine vs polyquat (or letting it ride, i guess, since it's cold now) for treating the remaining water for winter.

 

[ajw22]

Would still like any thoughts about chlorine vs polyquat (or letting it ride, i guess, since it's cold now) for treating the remaining water for winter.

I am a fan of a mix of chlorine and PQ for best insurance against a green pool in the Spring.

 

[superdave5599]

Cool cool. I thought I'd read last year that chlorine will oxidize the PQ (and therefore render it useless), so for winter it is advisable to go either/or.

 

[ajw22]

Cool cool. I thought I'd read last year that chlorine will oxidize the PQ (and therefore render it useless), so for winter it is advisable to go either/or.

Nope, the opposite...

Algaecide - Further Reading

www.troublefreepool.com

Even if you need to add Polyquat 60 when FC is above ½ SLAM level, Buckman Labs says that if the Polyquat is broken down by the higher chlorine levels it is still effective when used as an algaecide. Moderate to high levels of chlorine break down Polyquat but it still only transforms the formula into shorter chain polymers that are still just as effective.