Positive Results with Vitamin C Test

Stains on the pool surfaces, pool equipment or on the swimmers, or off-color swimming pool water. Discolored but clear water.

Positive Results with Vitamin C Test

Postby keno » Wed 15 Aug, 2007 19:01

I have been through an unbelievably ugly ordeal with my pool installer for a year relating to brown stains that appeared a couple of months after the initial re-surfacing to Sunstone. Rather than go through the entire ridiculous story about what I was told and how my pool is roughed up from a severe acid wash, I'll focus on that the fact that this website has taught me in one day, more than I learned from my local Pinch-A-Penny or pool installer in a year.

I did the chlorine and vitamin C test tonight. The chlorine did nothing, but three 250g tablets of vitamin C cleared up about three square feet of brown pool surface and it's now the nice Blue Lagoon color I paid for. One note though: I left the tablets in place for about an hour, and the surface turned black where the tablets were, with bright blue all around it. Is this normal? Regardless, it's hard to believe that a stain so stubborn and difficult to remove with pool acid in an acid wash will come clean with vitamin C!!! I'm amazed, and that's great, but now what do I do????
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Postby Backglass » Wed 15 Aug, 2007 19:37

The stains are caused by metals. Now that you have verified that vitamin C will work, you need to follow the procedure outlined on THIS PAGE.

You must follow the procedure as described or the stains will come right back with your next shocking.
===============================
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Download Bleachcalc free at troublefreepool . com /files/BleachCalc262.exe and start saving money on chemicals.
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Postby chem geek » Wed 15 Aug, 2007 21:02

Vitamin C is ascorbic acid which is a reducing agent (opposite of chlorine which is an oxidizing agent). This works best when the chlorine level is low, otherwise the chlorine will react with the ascorbic acid before the ascorbic acid gets to work on the metal stain. The ascorbic acid works best on iron stains by reducing the iron from a solid ferric state (oxide or carbonate) to a more soluble ferrous state and the acidity helps in this process (but an acid wash alone will not reduce the ferric to ferrous which is why it's not as effective), but as was pointed out you also need to add a metal sequestrant to hold this ferrous ion in the water so it doesn't get oxidized by chlorine and precipitate (stain) out again. Follow the procedure in the link that Backglass gave you.
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Postby keno » Wed 15 Aug, 2007 21:16

Sorry, I didn't mention previously that the pool is salt and uses a SWG. Is this procedure good for a salt water pool?
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Postby chem geek » Wed 15 Aug, 2007 22:48

Yes, the fact that it is an SWG pool with higher salt levels doesn't change anything. Most SWG pools tend to have the pH rise so would be more susceptible to getting metal staining IF there are metals in the water, but the same thing would happen after shocking with a hypochlorite source of chlorine that would temporarily make the pH rise (until the chlorine got used up).
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Postby keno » Wed 22 Aug, 2007 17:51

Everything is going very well. The stain is gone, my PH is at 7.2, and I've started to add liquid chlorine. What is "slowly," when referring to how fast to add it? Also, the article stated running the filter 24/7 - to be sure, this is suggesting running the filter 24hrs. a day for a week?

I have a SWG, but I'm concerned about using it at this time. I'm not sure what the effect electrolysis would have on the numerous chemicals added in this process. Any ideas about it?
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Postby chem geek » Wed 22 Aug, 2007 18:08

If the stain is gone AND you added a metal sequestrant to keep the metal in solution, then turning on the SWG should be fine. The pH will rise, but the sequestrant will prevent the metal from staining again. The reason for having the pH rise up slowly is that IF there isn't enough sequestrant, then you'll start to notice staining or colored water again and can stop making the pH rise (by turning off the SWG, for example) and add more sequestrant at that point.

Running the SWG will cause the pH to rise so you shouldn't need to add any chemicals to make that happen.

The 24/7 for the pump is during the stain removal process. Once the stain is gone and the metal sequestrant is in the water, then the pump needn't be on as long and you can return to normal pump times.
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Postby keno » Wed 22 Aug, 2007 18:20

Sorry if I wasn't clear about it, but the article mentions adding chlorine slowly. How fast is slowly? I added about 1.5 gallons today but still read 0 ppm.
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Postby chem geek » Wed 22 Aug, 2007 19:22

Sorry, I misunderstood as well. They mean to add chlorine a little bit at a time so as not to have the pH jump too high too quickly (for the reasons I stated). Adding enough chlorine that would normally raise the Free Chlorine (FC) level by about 4 ppm would raise the pH around 0.1 or so. That's about as much to do at a time. You always pour slowly over a return -- nothing new about that. The slowly they refer to is not to dump a whole bunch (gallons at a time) because that would raise the pH too quickly.

However, as you found out, the chlorine gets used up quickly at first because it is consumed by the ascorbic acid in the pool. So you can keep adding chlorine until you get a reading -- you don't have to wait in that case. Add enough to raise by 4 ppm FC, then wait 20-30 minutes and measure the FC. If you don't get a reading, add another amount to raise by 4 ppm FC, etc. Once you get a reading, you can wait to not add more chlorine until 4 or more hours later and you see that the water isn't colored nor any restaining is occurring.
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Postby keno » Fri 24 Aug, 2007 20:12

Pool's stable and done at this point. It looks perfect. Can't thank you guys enough for the help. Much appreciated.
Regards. :D
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