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Thread: Ascorbic Acid staining plaster black

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    Ascorbic Acid staining plaster black

    I’m a rookie, recent pool owner. My plaster turns not white, but black(!) when vitamin c tablets touch light brown-tinted stains (about 2 inch circle). I hit the internet, and I now understand conceptually “dissolve the metallic solids with Ascorbic Acid, then keep them suspended with sequestrant.” I also think I understand that high pH is conducive to metals coming out of solution (staining) and very low pH is conducive to dissolving metals into solution from the copper heater elements.

    Two questions: One, can I somehow “flock” or otherwise get the metal out (after Ascorbic Acid then sequestrant treatment in order to backwash out of the filter or direct to waste), even though it’s not algae and the water is already clear? (In other words, I’m looking for a long-term low-maintenance approach of metals/chemicals that I should aim at before just dumping chemicals in. I don’t simply want a precarious balance that works temporarily--but which needs a lot of time, attention and chemical$$, forever. Therefore I assume I need to get rid of metals, and not just keep them “sequestered” in the water.)

    Two, what is the risk of treating as if there are metals in the water, and it turns out the tests are right, and there are none?--I’m not exactly thrilled with the idea of adding more of that (Ascorbic Acid) which turned my plaster black!
    This staining is similar to others who have posted here (and I have learned a good deal from the following threads):
    2008: “The vitamin c tablets started to roll to my deep end and along the way (you will not believe this) turning my pool [plaster] black again everywhere they ran (like fingers reaching out).”http://www.troublefreepool.com/black...elp-t8327.html
    2011: “Found a brownish stain near the steps on the pool. Rubbed the [vitamin c] tablet onto it and the stain turned black.” http://www.troublefreepool.com/ascor...ck-t36452.html
    2009: “The [vitamin c/ascorbic acid) tablets turned the plaster black in a 6 in circle on one of my steps… About 30 min later … was shocked at what the spot looked like. It was the whitest and cleanest 6 in circle in the whole pool…” http://www.troublefreepool.com/ascor...ins-t2298.html

    For my own pool, after 30 minutes, and after 1 day and vigorous brushing, the black stains from vitamin c tablets were only a bit less intense—still a dark gray.

    I had the water tested at pool store and the reading was zero copper. Other readings: Free Chl 2, Total Chl 2, pH 7.8, Total Alk 160ppm, CYA 0, Calc Hardness 250, Total Dislvd Solids 2800, no reading on phosphates or iron. I have 30K gal., sand filter, chlorine puck float. The pool is 30 years old and I’m suspecting 30 years of hidden metal build-up on the plaster, but little in current water. I’m even wondering if the original cement/plaster was mixed with high-metallic water, but the plaster doesn’t seem to turn dark where vitamin c only touches unstained areas—so I guess that tends to rule out metal inside the plaster as an issue. I just backwashed in case there were excess metals in the sand.

    BTW, after my first chlorine shock, pool water turned from clear blue to clear green-blue (suggesting metals I assume); now it is back to clear blue. Right now, pool is not heated, about 65F, and under a type of pavilion (very low sun, low debris). I’ve been aerating with nozzles pointing up to help lower pH (to low 7’s, I hope) without chemicals.

    Finally if Chem Geek or anyone could tell me why A.Acid would turn plaster or metals on plaster black, I’m very interested. Thanks for any responses—y’all have helped me already from other thread answers!

    30K gal, plaster, sand, floating chlorinator
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

  2. Back To Top    #2
    JasonLion's Avatar
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    Re: Ascorbic Acid staining plaster black

    Ascorbic acid works best with iron stains. AA is not a good treatment for copper stains, which may appear somewhat similar to iron stains. When you use AA with copper stains, the stains may lift off, or they may turn black. When black they are often even more difficult to remove then they are when tan/brown. Turning black is a result of a change in the oxidation level of the copper. Several oxidation levels are possible, resulting in several possible colors for copper stains. The best treatment for copper stains is an acid wash.

    There is no universally reliable method for removing metals from the water. There are various approaches that work some of the time. Generally the best thing is to keep the metals out of the water in the first place, or use sequestrant regularly.

    Copper can turn the water green when you raise the FC level significantly. Occasionally high FC levels will cause the copper to form crystals large enough to be filtered out.

    Presumably there isn't any copper in the water right now because it has all deposited as stains. When you do manage to remove the stains, the copper will be back in the water.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. Back To Top    #3

    Re: Ascorbic Acid staining plaster black

    Thanks for the comments. Emptying pool and acid washing is not an option now. "There is no universally reliable method for removing metals from the water." ouch.

    Any advice for how high FC should be to hope for crystals? My tentative plan would be to load up DE into skimmer, raising the pressure 2-3 psi to make sure the DE is in place, shock like crazy, wait for crystallization (how long? what would it look like? anything else to do to optimize chance for larger crystals?), filter for x? hours, then backwash. (or perhaps change top layer of sand, then backwash?)

    How does that sound?
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

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    Melt In The Sun's Avatar
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    Re: Ascorbic Acid staining plaster black

    It sounds like you're going to probably end up with more stains. I've never heard of anyone successfully crystallizing metals and filtering them out of their water.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Re: Ascorbic Acid staining plaster black

    It's also not the chlorine that causes the precipitation (or staining) of metal, but the high pH. Chlorine will oxidize ferrous ion to ferric ion, but it doesn't take high chlorine levels for that to happen. It is raising the pH which causes metal ions in the water to form oxides-hydroxides and carbonates. As was noted in the previous post, one cannot easily control where the metal precipitation occurs. Raising the pH can just as easily cause the metal to stain a plaster surface as it can cause it to precipitate and get caught in a filter.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Ascorbic Acid staining plaster black

    "more stains" hmm.

    OK, I'll not risk trying to create crystals. I appreciate the oxidation/pH explanation.

    Anyone have any success using metal-out (not sure brand names) hose filters (usually for fresh well-water)? And can they be used successfully by just recirculating from a submersible pump back into the pool itself?


    ---
    30,000 gallon, plaster, pentair sand filter, floating puck chlorinator
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

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    JasonLion's Avatar
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    Re: Ascorbic Acid staining plaster black

    Yes the metal-out type filters do kind of sort of work, but they are slow, expensive, and significantly less efficient then they often claim to be. They work best at very low flow rates (think 1 GPM), usually remove significantly less than 50% of the metals in the water passing through them, and don't normally last as long as they claim to last (which is often fairly short to begin with).

    There are larger filters based on the same principals, that are also much more expensive, which can handle somewhat higher flow rates and remove more than 50% of the metals passing through, but with their added costs they are only occasionally worth the effort/expense.

    If the stains are limited to a small area, you can try putting some dry acid in a sock and holding the sock against the stained area for a little while and see how that works.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Ascorbic Acid staining plaster black

    OK, I will try the dry acid in a sock tomorrow and post tomorrow night or Saturday. Thanks for the suggestion.
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

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    Re: Ascorbic Acid staining plaster black

    I have talked to the guy who invented the CuLator metal removal bag. He claims to have the only product that actually removes metals from water. It is a bag placed in the skimmer and it will remove about 0.8 ppm of copper from about 25,000 gallons. Here is a website with some FAQs:

    http://www.culator.com/faqs

    No recommendation but it might help. It could be expensive.

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    Re: Ascorbic Acid staining plaster black

    We've written about CuLator in a few threads: CuLator Metal Remover, Culator - Does it work? and CUlator...ready to test. We don't have enough reports to be definitive about it so we don't recommend it regularly, but when it does appear to work it physically removes metal from the pool in terms of metal ion tests and not having staining returning. I think if it were less expensive then more people would use it and we'd have more reports about it.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Ascorbic Acid staining plaster black

    As suggested, I tried dry acid in a sock, rubbing it on some pool stains. It did not turn black! The two stains I tried it on both lightened in tint. They did not completely disappear, but they are faint enough as to not be unsightly.

    So does this mean I should try an ascorbic acid treatment, even though in tablet form it caused dark staining? or perhaps a dry acid treatment (just substituting for AA)?

    BTW, I checked out Culator at Amazon, it has a high rating from five of six reviewers as of 9/30/11. However, the five positive reviewers have the Culator as their only review. This doesn't prove the postive reviews are fake, but in general, one-review raters are less likely to be objective than others.

    Thanks again for the thoughtfulness of responses.
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

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    Re: Ascorbic Acid staining plaster black

    Quote Originally Posted by gcharles
    I’ve been aerating with nozzles pointing up to help lower pH (to low 7’s, I hope) without chemicals.

    I spotted that you are trying to lower your pH without chemicals by aerating. To let you know, areation increases pH. Usually you aerate to raise pH without raising your TA.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: Ascorbic Acid staining plaster black

    You don't want to use AA. It will turn everything black.

    It is sometimes possible to do a whole pool acid wash without draining. You have to either not have a heater, or be able to bypass the heater. If you try to do a no drain acid wash with the heater in the plumbing the heater will be damaged. It can also be problematic in that it will take some plaster off along with the stains. That is why manual application is preferred, you can control where the acid is placed and how much is used so you only take off what needs to be taken off. If you do this, you want to use muriatic acid, not dry acid.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Ascorbic Acid staining plaster black

    "Aeration raises pH, not lowers it." Yes, thank you, it's not the first, and won't be the last rookie mistake I make!

    "You don't want to use AA. It will turn everything black." Thanks. I was confused by this, since it seems to be such a common remedy. I'm sure you're right, based on how the AA tablets blackened my plaster. (I don't have a heater by-pass to try the muriatic acid-wash.)

    I have one new question and some self-reflection on my options.

    My question: Can I go heavy on the D.E. in my sand filtration? (raising pressure 2 to 5 psi?) Will that catch metals? I know the filter may clog quickly, and that I'd lose the D.E. as soon as I back-washed, but perhaps that's good if the D.E. becomes impregnated with iron and copper. If anyone has an opinion on this I'd love to hear.


    As I see it, my options are:
    -CuLator (I believe their skimmer pouch will attract some metals, but I'm skeptical that their process grabs enough to make any significant impact (there is no true filtering; also no trustworthy testimonials or independent analysis))
    -Hose "metal-out" filter; either with current water or fresh well-water (I believe these can have some effect, as per Jason/TFP admin--at a small fraction of claimed efficacy)
    -truck in water
    -experiment with extra DE in sand filter
    -experiment with home-made filters (this would end up being a big project)

    -Or give up on metal reduction, and focus on living "with the disease," but, "with as few symptoms as possible."
    This would mean more time and vigilance (and chemicals) to keep metals sequestered for as long as possible, and preparedness (installing a heater by-pass) to deal with eventual staining, and budgeting for eventual water replacement and further treatment.
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

  15. Back To Top    #15

    Re: Ascorbic Acid staining plaster black

    I recognize I'm leaving "chemistry"; but I still am wondering if (extra) DE in the sand filter can help with metals. (I'm also wondering if my last post was so late at night it wasn't seen.) I've been to the TFP standard instructions for DE/Sand, which recommends a 1 psi rise in pressure. Is anything gained from adding more DE?--except the risk that pressure may rise too fast beyond that? Again, is there any point at which DE traps metals or is this a non-starter? Thanks to anyone who has an opinion on this.
    30,000 gal. (18x38ft rectangle, bottom 9ft drain, plus 2 skimmers), gunnite/plaster, +small tiled spa w/spa drain&jets. Sand filter, floating chlorinator, .75HP Sta-Rite pump, 1.5in pipes, Raypak 265K BTU heater. Pool is 30yrs old, history of maintenance and re-plaster unknown. It is "indoor" (pavillioned--little sun). Plaster in fair shape, with a little permanent staining that did not come out in recent acid wash.

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