Metal Staining - a Seemingly Never Ending Problem

[bjpeters]

I have an above ground pool - approx 17,000 gallons and am having never ending problems with metal staining on the vinyl liner - have used the ascorbic acid test which quickly removes the stains but unfortunately only temporarily. Have not been able to determine the source of the metal contamination - have tested the city water used to fill the pool and that showed minimal iron and copper, do not have a heater, have a Hayward DE filter (almost 20 years old) and pump - all other piping is plastic. So, I follow what I have found to be the directions for removing the stains (along with the metals) but the stains re-appear within a few weeks. Does anyone have a good quantitative measure on exactly how much metal sequestrant to add? I have been using Metal Free (1 liter treats 20,000 gallons) but stains re-appear once the pH rises above 7.2 and the chlorine levels are about 3.0.
The procedure I have followed is to add ascorbic acid at rate of approx 1/2 to 1 lb per 10,000 gallons and watch for stains to disappear - pump is run 24 hrs. Once stains have disappeared, I add the Metal Free (this time added a total of 2 liters) and let the pump circulate. I have no available chlorine at this point due to the addition of ascorbic acid and will start to add chlorine slowly after 24 hrs. I will continue to watch my pH and slowly adjust upward. I have been told no shocking for at least 2 weeks. I have used this procedure repeatedly, the stains disappear for a short time only to return. Guess I am looking for a more permanent fix to this problem - this is very frustrating! I would understand some of this if we had well water but that is not the case. Any suggestions will be much appreciated. Thanks.

 

[Bama Rambler]

How do you chlorinate.

If you use tabs a lot of them have copper in them as well as a lot of feed systems.

 

[bjpeters]

I use the 3" tablets for chlorine - so could that really be more source of metal? Not really sure what you mean by "feed systems".
Generally I use the 3" tablets in the skimmer basket - so if I can't use the tablets, what do you use for chlorine?

 

[Bama Rambler]

We advocate the use of bleach or liquid chlorine (which is the same thing). Look at the ingredients on the container of tablets that you use and see if they contain copper. Also take a sample of your water to a local pool store and have them check it for metals.

 

[JasonLion]

Metal Free is not one of my favorite sequestrants. It seems to be noticeably less effective than others. ProTeam's Metal Magic and Jack's Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) are some of the top sequestrants. You can also find many other brands with similar products, some of which are noticeably less expensive. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.

 

[bjpeters]

If I use a product like ProTeam's Metal Magic am I going to have problems with cloudy water due to the precipitation of the metals?
Looks like you do not have to worry about lowering the pH for the Proteam's product, correct? Is this actually going to remove pre-existing stains or just prevent new stains from forming?

 

[JasonLion]

Any sequestrant will remove the occasional existing stain, but for the most part they won't affect existing stains. Seeing a little clouding after adding sequestrant the first time is normal, and should go away after two or three days. Subsequent doses should not cause clouding. Precipitation of metals is rare, though it does happen. More commonly it is calcium that precipitates.

 

[smallpooldad]

bjpeters,

Like you I to had a never ending issue with iron stains re-appearing after the AA treatment, even after complete drains. Our iron is primarily deposited by airborne volcanic dust, there may be some in the fill water but I am guessing not much as toilet bowls and sinks do not stain, we have no copper issues. Although some pools in Hawaii, older than 20 to 25 years, do have copper plumbing and therefore copper issues as well. The pool heat pump (not used often) is Titanium lined.

I also noticed that if I kept my pool at a pH of 7.4 or above these stains would re-appear, at 7.4 slowly at 7.6 quickly. It might be our very soft water so you may be able to get away with 7.4.

Now I keep my pool at a pH of 7.3, the only problem for me, as I have an in-ground gunite pool, is to keep the CSI in the safe zone (-0.30 to 0.00) with a alkalinity now maintained at 70 ppm (naturally it goes to 60 but I do not wish to add too much calcium) it required me to up my Calcium Hardness (CH) to 625 (after two weeks please see below). So when I backwash I lose about 3% of this so I need to add calcium, to control the CSI index. I think that this calcium issue is not such a great concern in vinyl liner pools.

You might, however, wish to ask on this forum for recommended balance numbers based on a vinyl pool with a pH 7.3 or 7.4, dependant on your choice of number.

In the treatment for iron using AA I think the post mentions it is a good idea to keep the pH at 7.2 for a week or two, I guess this gives your pool a mild acid wash. Note here I did not up my Calcium from 350 to 625 until the end of the two week period, this kept my CSI below -0.40/-0.50 thereby extending the acid wash cycle. Doing this for 2 weeks definitely helped. The other thing that also helped greatly was Jack's Magic "The Purple Stuff", as I have a SWG, I am not sure of the appropriate type for non-SWGs. Of all the sequestrants I have used this seems to the only one that works, and I have tried many, but not Pro-Team's, unfortunately it is not inexpensive. In my 10,000 gallon pool after the initial 32 oz dose I add 12 ozs weekly. So far so good, plus what faint light stains that still remain seem to be lifting slowly.

After the initial AA treatment and after having added 32 ozs of "The Purple Stuff" after the first 12 hours, 2 days later, I backwashed my filter and even though the pressure had not built up by very much, it removed a lot of white particles. I again back washed the filter week later and again a lot of white particles were removed, whether or not these contained iron I do not know. But the "Proof is in the Pudding" and at present no iron has re-deposited that I can see. Normally I backwash once a month and will do that again when I stop seeing this many white particles every week. My guess would be that it is scaling being removed from the walls during the mild acid wash.

Other things that I learnt over the years are to always mix my chemicals in a bucket before pouring them into the pool, except CYA for which I use a sock in the skimmer. And for salt I punch many holes in the plastic bag and hang it on a pool cleaning rod in the water so that it dissolves before touching the surface. For me, Borax, Baking Soda, and sometimes Calcium, if unmixed can create spot stains where they fall on the gunite, and try to spread the introduction of large amounts over a half-hour or so intervals, I do not know if that also helps.

Other numbers my CYA is 30, FC is 5 - 6, Salt 3400 ppm.

Finally one last thought, I would imagine at some point in the future, when I do not know, there will be just too much iron in the water for even the excellent "Purple Stuff" to handle, and the stains might slowly return. I am planning on buying an iron test kit to ascertain at what level that might occur and then being forewarned will drain the pool close to when that level is achieved in the future. By drain the pool I do not mean a complete drain as I have done in the past but to a safer level, to a point where I might have a year's worth of insurance. I should be able to know this year's worth of insurance by calculating how much iron my pool increases by monthly in ppm and reduce by ppm times 12, draining the pool by that percentage. I suppose it is always possible that the sequestrant might keep up indefinitely but I doubt it. Others on this forum more knowledgeable in chemistry than I might know exactly what will happen in the future and might care to comment. I think this is known as the "Saturation Point", but I am not sure of the exact terminology.

Hope these experiences can be of help to you.

 

[smallpooldad]

Jack's Magic "The Purple Stuff" for SWG

I spoke with Jack's Magic Tech Support and I should not have raised the CH from 350 to 625, nor allowed the pH to go above 7.2. They suggested keeping them at these lower levels to slowly remove all impurities for up to 10 weeks or even longer, brushing daily, twice or more being preferable.

It seems to me that if one has scaling, the iron seems to settle on the scaled portions more so than on the areas without scaling, any thoughts?

When I raised the CH it wiped out the Jack's Magic according to the tech.

Well I learnt something.

One lady tech I spoke with stated that the iron would be slowly removed as white powder, this is the powder I saw in the backwash, but I was under the impression from this site that iron can never be removed but only put into solution. Does anyone know for sure or is this partially correct?

 

[JasonLion]

Iron is occasionally removed, but not reliably enough to depend on it. The white powder is almost entirely calcium, though there may be a little iron in there as well.

The higher CH level doesn't exactly wipe out the sequestrant as much as it overwhelms it. Sequestrant works on calcium, which is technically a metal, as well as on iron. At high CH levels, the sequestrant tends to bind with calcium before it runs into any iron, and then stays bound to the calcium. The sequestrant is still there, it just isn't being useful.

Iron stains tend to deposit on areas where the surface is rough, which is very common with calcium scaling and rare for a properly made plaster surface. Worse, iron often gets incorporated into calcium scale, actually binding right into the calcium, rather than just sitting on the surface, creating a layer that can't usually be removed using conventional metal stain treatments.

 

[bjpeters]

Another question regarding the use of ProTeam's Metal Magic - do I have to be concerned with the FC level when I add a quart of the Metal Magic? The label indicates FC should be at or below 1 and you should not plan on superchlorinating for 7 days - is that true? I want to remove any metals in my water but am afraid to add the Metal Magic while I am still in the process of shocking the pool. Suggestions?

 

[JasonLion]

If you want to remove metal stains, you need the FC level very low. But if you are simply adding maintenance doses of sequestrant it doesn't really matter what the FC level is.

 

[bjpeters]

I was looking at adding a quart for 16,000 gallons - do I need to worry about FC?

 

[bjpeters]

Ok, thanks for the reply.

 

[Swampwoman]

Since this thread is fresh and germane, I thought I'd jump on here. I have just rehabbed my foreclosure pool and gotten it stable, reduced TA to 70, etc. During the rehab, many of the stains disappeared and from a distance, pool looks great. I had added sequestrate, and I've started using a filter on my fill hose, as I am on well water that does indeed stain my toilet even after being through the softener. I have very faint stains along the channel where the leaves sat fir a few years which you can now only see if you look closely, and figured I'd let the sun and chlorine over the season fade those (or reveal they are metal, as the case ay be.)

However, I have 3 spots in the shallow end the size of coins and a larger one the size of a fist that are clearly iron, plus my stairs are discolored -- these were there on opening. My skimmer is only very lightly stained by comparison. I think overall I may have reduced the iron in the actual pool water through so much backwashing and pre filtering (don't have an iron test, guess that's the next aquisiion the local pool place said no metal problems in the water using their test, which of course I don't trust, because I know my well water

If I use jacks step stuff, do I need to drop the FC? Since I would need to spot treat the three stains with ascorbic acid in a sock anyway, should I just do that on the stairs? With spot treating, do I still have to drop the FC? I'm trying to avoid dropping the chlorine or otherwise rendering the pool out of commission, but the weather is pretty cool again right now so this stretch might be my best chance.

I welcome suggestions!
Thanks and cheers