Ascorbic Treatment to rid Pool of metal stains

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geekgranny

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Aug 20, 2009
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North Central Texas
How about brushing the pool sides and bottom during treatment? When and how often? Okay to use the SS brush?

I'm hoping some of the scale will begin lifting too. I only switched to BBB (minus the borax because of dogs drinking from pool) a couple of months ago. The scale was deposited in the past year prior to BBB, as I acid washed last fall. When doing the acid wash we didn't do the bottom too heavily as it was really thick there in some areas and I didn't want to cause any pitting in the areas that didn't have as much scale. I know from experience about pitting on horizontal surfaces (even slopes too) as I have one small pit on the top step from last years acid washing. The only way I could get the scale off of the steps without damaging the blue plaster was to use an angle grinder with a concrete disc. Took me a few hours to do the bottom step but didn't get the other two done due to an injury while doing the AW. :cry:

Thanks, gg=alice
 

geekgranny

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Aug 20, 2009
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North Central Texas
frustratedpoolmom said:
Brushing isn't always necessary...
Thanks, Mom. Glad to hear that. I want to start the treatment tonight but have to backwash first. Since I switched to BBB it seems that some of the scale is lifting from walls. :-D

I had to make a stop by pool store today to pickup a couple of return rings (mine are so old they crack when I screw them tight. Anyway the manager, the one who was supportive of me, a few weeks ago, when I told him I had switched to BBB, told me to be really careful using the steel brushes, especially while doing the AA treatment. My plaster is 13 yrs old. He also cautioned to make adjustments on the Wall Whale so the brush doesn't dig in too much. I posted, earlier today, about finding the Brush Booster, that is a fin that can be used on any pole/brush to give some of the benefits of the Wall Whale.

Off topic.... He has an 80 sq ft, Hayward DE filter that was a display model in a setup showing typical, whole pump station, with multi port valve included that he will give me a good reduction of price on. Leslie's corporate wanted the stores to display a smaller filter; I guess so as not to scare customers.

He was in the field for many years and advised me about the cost of replacing the four cartridges on the Pentair quad and other parts. He likes the Hayward filters better and thinks they are more robust. I also purchased another bag of cellulose for my current DE filter. I told him I haven't yet decided whether to stay with it as I'm not sure it is filtering any better although one indication that it is is that I have to back wash more frequently than when I was using DE. He said he thought the cellulose did improve filtration. If I do go back to DE I'm going to have to get some type of separation vessel or use a SlimeBag to keep from putting any more DE into our sensitive habitat.

gg=alice
 

clutch8888

Member
Oct 19, 2009
8
Hi Folks,

Seems the recommendation to keep the stains away after absorbic acid wash is to keep the PH on the low side 7.0 to 7.2.
Would keeping the PH that low long term have side effects? Its the low end of the usual recommended 7.2 to 7.8 range

thanks
 

geekgranny

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Aug 20, 2009
1,358
North Central Texas
duraleigh said:
absolutely none. Into the 6's for long periods is a no-no. 7.0 for as long as you like is fine.
Glad to hear that. Just recently did the AA treatment. Worked great except for a few areas on walls that might be copper staining. It took the iron staining longer to lift from the heavily scaled area on shallow end bottom than any where else. Actually anywhere the stain was on scale it took longer than on plaster. There was a light tan stain still left, shallow end floor, when I started readjusting levels back to normal and bringing chlorine up slowly. It eventually lifted even after I had finished the intense AA. I've been keeping pH slightly above 7, using sequestrate, and it seems to have not come back. :party: I've been brushing a lot more than usual and it seems the scaling is still releasing too.
 

carolina pool

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May 7, 2009
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Charlotte NC
A couple of questions:

Wouldn't it be best to also treat the sand bed when doing the aa treatment?

Would it be a good idea to drain the the pool after the AA treatment to remove all of the metals and phosphates?
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
Draining a pool can be dangerous (depending on type of pool, location of water table, etc.) and water can be scarce or expensive in some areas. Nevertheless, significant dilution can usually be done safely and spreads the cost over time.

There are some products that claim to coagulate metals to capture them in the filter, presumably clumping together the metal sequestrant particles so they can be filtered and backwashed, but I haven't seen any reports about their effectiveness on this forum (that I can recall).

As for phosphates, they are not a problem if you maintain sufficient chlorine levels. My pool (shown here and here) has had 2000-3000 ppb phosphates, yet I prevent algae growth using chlorine alone (until this year -- I added 50 ppm Borates, but for 5 years previous to that I used chlorine alone). Nevertheless, I still use winter rains to dilute my pool water, mostly to keep the slow salt level buildup in check and to dilute whatever chemicals there are from bather waste that don't get fully oxidized.

Richard
 

carolina pool

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Thanks Richard, I was hoping you would reply.

In this case it is safe to drain the pool and the cost to refill would be around $200 plus it would make a simultaneous coping repair easier. It is 20yrs old with the original white plaster still in very good shape. 10+- years ago we drained and cleaned the stains. (didn't know about AA treatment then)

I have had several customers do the AA treatment on thier own with different levels of difficulty and success but without the benifit of the good instructions provided on this forum. It seems that once the stains are back in solution draining the pool would make it easier on the customer for future maintainence.
 

Beez

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May 19, 2009
785
Dallas, TX
renovxpt said:
It seems that once the stains are back in solution draining the pool would make it easier on the customer for future maintainence.
Unless the source of the metals was the fill water!

I have mild iron staining in my pool, and I was thinking along the same lines as you are, to do a drain/refill after the AA treatment. But then I started thinking about how the iron got into the pool in the first place. Isn't the fill water the likeliest suspect?
 
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carolina pool

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Beez, I think you are right. In this case it seems that an entire area of town has more problems than most and I have guessed that the main supply line must be ductile iron? The city flocs metals out when treating the water and the tap water doesn't test high enough to measure the iron, so I think it might be trace amounts over time that attach when the conditions are just right.

Unfortunately I had a lousy high school chemistry teacher and that part of my brain doesn't work well enough to follow most of chem-geeks explanations. It sounds like ascorbic, citric and phosphonic acids put the iron back into solution and create potential food for algea. It also seems that if the conditions are right all of that iron can come back out of solution and reattach. The latter is consistent with my experience I hope that Richard can explain it, he certainly knows the answer.
 

JasonLion

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Ascorbic acid converts iron staining into dissolved iron in the water. Phosphonic acid (and other sequestrants) bind to the iron dissolved in the water and prevent it from redepositing as stains. However the phosphonic acid breaks down over time, so you need to keep adding more to keep the iron in the water. To some extent phosphonic acid can remove stains, but it isn't any where near as good at doing that as ascorbic acid is.

When there is iron in the water, low PH (say around 7.0 to 7.3) tends to prevent staining while high PH (say around 7.8 to 8.2) tends to cause staining. Phosphonic acid helps control this, so that high PH levels can occur without staining. High FC levels also tend to cause staining. As the PH goes up, and/or the FC level goes up, the chances of staining increase. Likewise, as the phosphonic acid level goes down, the chance of staining increases.
 
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carolina pool

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Thanks Jason, Maybe some clarity is coming. So is it correct to assume:

Ascorbic acid puts it back into solution with minimal or no effect on phosphate levels?
Phosphonic acid keeps it in solution with an increased level of phospates and buffers the effect of high PH?
Does that mean: if you use a phosphate reducing product it will counteract or break down the phosphonic acid thus releasing/increasing the potential for iron staining?

If you drain the pool after the AA treatment would'nt this substantially decrease the potential for recurring iron staining by removing the iron in solution and also reduce the need for phosphonic acid as rountine maintainence?

I am still having trouble understanding the purpose of putting the filter in recirc during the AA treatment.

My priority is to keep it easy on the owner. His plaster is in great shape and if he can continue with the routine he has used for the last 20+ years and get another 10years before replastering, he will be a happy owner.
 

JasonLion

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renovxpt said:
Ascorbic acid puts it back into solution with minimal or no effect on phosphate levels?
Phosphonic acid keeps it in solution with an increased level of phospates and buffers the effect of high PH?
Does that mean: if you use a phosphate reducing product it will counteract or break down the phosphonic acid thus releasing/increasing the potential for iron staining?
Yes, yes, and not exactly.

Phosphonic acid breaks down over time, leaving behind phosphates. Using phosphate remover shouldn't speed up that process, just get rid of the already broken down phosphonic acid. On the other hand, constant use of phosphonic acid is going to mean constant use of phosphate remover, which makes it even more annoying and expensive than it already is. There are some phosphate free sequestrants, but they are much less effective than the ones with phosphates.

Replacing the water with metal free water is the best long term solution by far. That is assuming you can get some metal free water. The metals in the pool must have come from someplace. Usually they come from the fill water. "Draining" the pool is one of several ways to replace the water, not usually the best choice however.

Putting the filter on recirculate helps avoid the small chance of coating your filter media with metals, which might end up forcing you to replace your filter media. This doesn't usually happen, even if the filter isn't on recirculate, but best to avoid even the small chance of a problem by using recirculate.
 

carolina pool

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Jason,

Thank you for the response and this great website! Your 'Mythbuster' atitude is very refreshing and appreciated. Chem-Geek and Mas are my favorites but the whole contributing group is awesome! Thank you.

Your cautious advice about draining swimming pools is very sound and it is not my intention to promote otherwise.

In regards to the filter: Are we assuming that there is a nominal amount of iron already attached to the sand and it would increase from the AA treatment? In my way of thinking the sand in the filter would be the same as the plaster and should be treated the same way?

Rod
 

carolina pool

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One more question.

When doing the AA treatment is there any etching of the plaster? and if so how would it relate to a traditional acid wash using muriatic?
 

JasonLion

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Ascorbic acid is way way way milder than an acid wash. There won't be any plaster etching, though the metals coming off can change the texture of the surface.

As far as the filter goes, normally any iron in the filter would be removed. However, there are rare cases where something else happens. With a lot of iron in the water, stains can form very quickly under the right conditions. Remember, this isn't at all common. The whole goal of the treatment is to avoid those conditions. However, if something goes seriously wrong, you can deposit iron very quickly. If that happens inside the filter, the filter media can be destroyed. If that happens just about anywhere else then you are back where you started, which isn't good but also isn't terrible.
 

polyvue

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abigail07 said:
I just want to say thank you for that information. It really helpful because we all love a good swim in the afternoon or during the summer season. But what will happen to our pool after winter? We should always expect for the unexpected, and that is the Stains!
Welcome to the forum, Abigail... :-D

It's wise to be prepared for anything, to the extent that is possible, but stains are usually quite preventable. Check out some of the articles regarding pool chemistry, here.
 

DLSDO

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Sep 27, 2007
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Midwest
Took a little different approach. I wanted to share it with everyone.

Had a big "ring" of metal staining around the perimeter of the pool at the winterized lower water level. Very unsightly.

This is what I did...

  • I did not lower my FC[/*:m:1qkbbiz4]
  • I first added sequestrant in appropriate levels[/*:m:1qkbbiz4]
  • Then I bought 16oz of AA 5000mg/5cc powder[/*:m:1qkbbiz4]
  • I placed the AA in a sock and worked my way around the perimeter of the pool and spot treated as necessary[/*:m:1qkbbiz4]
  • The staining vanished with a light rub[/*:m:1qkbbiz4]
  • It dropped my pH and TA a bit[/*:m:1qkbbiz4]
  • I immediately brought it back into range with Baking Soda[/*:m:1qkbbiz4]

Pool looks great

Few comments....

All this pool stuff is just like a big chemistry lab. The goal is to get the precipitated metal off the pool surface and sequestered in solution.

In my situation it seemed to make more sense to use AA sparingly so as to minimize cost, decrease risk of an algae bloom, decrease time away from swimming and lessen excursions of pH/TA. As long as there is adequate volume of sequestrant to bind the metals then new staining should be minimized.

This certainly won't be ideal for all but I wanted to let you know what worked for me.

Hope that helps :)
 
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