Quarter sized oval shaped ringed rust stains on bottom of pool . . .

[chem geek]

The best way to test if they are metal or organic, is to crush up a couple of vitamin C tablets, put them in a sock, and rub them on the stain - if they go away, it is metal. You could also use ph down and do the same. If they don't go away with either of these methods, then I would try the same thing with a crushed up triclor tablet, rub it on the stain, or hold it on the stain. If they lighten then they may be organic. There is also a stain test by "Jack's Magic" that can help you tell what kind of stain it is. You can also try a stain stick that is sort of like a rubber coated pumice. To take the rust off your metal, I would suggest using sand paper. I don't know how or why it rusted - but sand paper should take it off. You can put a dose of metal sequestering agent in the water to bond with any metal that is in suspension. Your chemistry looks perfect to me now. However the stains could have formed some time that you had high chlorine levels along with high ph levels, this will let any metal that is in the water fall out and stain the surface of the pool. The sequestering agent hold the metals in suspension, so they do not cause stain on the pool. I am checking out a product that is supposed to react with the metals and turn them into crystals, therefore allowing the metal to be filtered out, instead of just staying in solution. It is by Proteam, and is "Metal Magic". Feel free to ask any other questions you may have.

Thanks for the fantastic advice. In fact, on the advice of my friend in the industry, I did rub/crush a trichlor tablet onto one of these stains and had the trichlor tablet rest on the stain for a time to see if it would fade, which it did not. So that implies that it is a metal stain and not organic (i.e. not algae) which is good in some sense. I'll double check this with the crushed vitamin C tablets in a sock, as you suggest. I may have to get my scuba gear out as most of these stains are at the bottom of the pool in the deep end. Seriously, I think there's a stain I can find that is more easily accessible.

Would it be worth my having my pool water checked for metals? If there is a continued source of rust shouldn't that be detectable in such a water test?

Thanks,
Richard

[waterbear]

your water may or may not test positive for iron if you have staining. If the cause of the iron was not a continuous one and the iron has already deposted as stain then you will very probably test no iron in the water.

[chem geek]

Well it took me a long while to do it, but I finally got around to getting some cheap Vitamin C that was mostly ascorbic acid with minimal extra ingredients (starch, etc.) and I crushed them, but them in a sock, and rubbed the stains at the bottom of my pool. Nothing happened. Tri-Chlor didn't change the stains either. I also tried rubbing the tablets directly rather than crushing them and again nothing.

I also tried this on a stain I KNOW to be metal (rust) since it is right where the metal bars are that had their insert fittings rusted from my use of Tri-Chlor in a floating feeder over a year ago and it looks reddish just like rust. The Vitamin C just didn't get rid of or even fade the stain.

So for whatever reason, it didn't work for me. Perhaps the stain is so old that it has permeated the plaster/gunite too far for the ascorbic acid to get rid of it. I'll see about getting "Jack's Magic" assuming it's more than just ascorbic acid.

Richard

[smallpooldad]

These stains appear to be the same as ours

They do not go away with any treatment we have tried so far egg. Ascorbic acid method, high chlorine - 40 ppm for 1 week, stain removers, and the oxalic acid method. We never really removed any stains for 9 years, as we had no idea how to do this, until we found this website.

We use to chlorinate with Tri-Chlor tablets and had a Nature 2, we removed the Nature 2 and now chlorinate with liquid chlorine and recently started using Borax. So the pool was way under chlorinated for 9 years based on high CyA. This is why I hardly ever swam in it as I got ear infections. Now at the correct chlorine (6 ppm) for a CyA of 50-55, I never get them and swim daily.

Although the ascorbic acid method did turn the plaster from brown to white it left it with the faint dollar stains you describe, probably there all the time hidden by the brown iron stain. Like you, we believe that they are impregnated into the plaster from years of neglect.

Needless to say they could be caused by some other metal, but what that might be we have no idea.

A week or so ago we added Borax to 70 ppm, for pH control, and this did help lighten them. We also scrubbed the plaster pool with a stainless steel brush and again this helped to remove some but not all (cloudy pool for two days). It did lighten them.

Some years ago, a neighbor of ours had this same problem. They drained the pool and then had a company come out and sand down the pool with an electric orbital sander using 300 then 500 then higher numbers wet/dry sanding paper from 3M (similar to that used on cars). There pool surface is very smooth so presumably they must have used 1000 or higher grit to get there.

If you do try this, very gently run a tiny trickle of water down the side you are working on, make sure the sander is plugged into a ground fault interrupter and wear thick rubber boots used by anglers and electrical workers. In addition long rubber sleeve electrical workers gloves might be a good precaution.

It did do a good job of removing the stains and of course a small layer of surface plaster. Doubt if it is rebar; if it were it should be then occurring throughout the pool.

Hope this helps, would be good to know how it goes if you try it. Like the bottles say, in fine print, try it in a small area first.

Aloha

[mbar]

I don't know why, but rust does not seem to come off with ascorbic acid. You can try using a stain stick, or some fine sand paper to rub the stain. It will take off some of the surface, but not enough for it to matter and it will get rid of the stain. You can also contact Jack's Magic, and ask them. They should be able to answer the question.

[chem geek]

I contacted Jack's Magic and I must say that these guys are quite knowledgeable about stains (even knew some chemistry, which surprised me). Anyway, for rust they recommend an oxidizer first (they use something that sounds similar to a non-chlorine shock like KMPS except higher in oxygen content) and then a stain remover that sounds like dry acid (possibly sodium bisulfate). I'll get some of their products and see what happens and let you know. I suspect that ascorbic acid just isn't strong enough by itself.

Richard

[waterbear]

If ascorbic acid doesn't work on rust then oxalic acid might. It is a commen treatment for rust stains outside of swimming pools and is the ingredient in some pool stains revmovers such as 'Stain Treat'.
Richard, Jack's Magic knows their stains! They don't list the ingredients in their MSDS, however but I suspect that the oxidizer that they use is sodium percarbonate.