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

[treiher]

Was just doing a quick search on the internet and stumbled on to this forum. Looks like a great resource!! Anyway, we just had about 15 or 20 new stains appear this summer on the bottom of our 3 year old plaster pool. They are ring shaped, which are oblong (not round). Sort of like a skinney "0", if that makes any sense. I am concerned that this might be rebar bleeding through the plaster, but I sure don't remember seeing any rebar sticking through the gunite when the pool was being constructed. Is this a common problem? Does anyone no what it looks like if it occurs? I have tried a stain removal chemical which I bought from the pool store, but unfortunately can't remember the name of it. I do remember it came with a pretty strong warning about using it with colored plaster. Anyway, it had no affect. One other remote possibility I am thinking is for awhile, there was about an 18" long piece of wire sitting on the bottom with the insulation stripped off on both ends. Not sure how it got in there, probably the dog, but we did not notice it for awhile. I'm wondering if that could have caused the stains as well, which I would be a much better problem I think than rebar stains, but I think that might be wishful thinking on my part. Any advise on this would be great appreciated. Thanks!

[chem geek]

Not sure if [treiher] still "active", but I was searching for pretty much what he described because I've had these spots in my pool pretty much since around the first year of use. Now after being on this forum, I'm ready to tackle it.

I have a small number of these oval shaped brown spots no longer than a quarter size in diameter (and the narrow side is much narrower than that -- about the width of a pencil or a little larger). Most have occurred in the deep end of the pool on the sunnier side, but I see others in a few other places as well. This had me thinking algae at first, but I'm pretty sure it's a metal stain.

We have two stainless steel metal bars in the pool (under the water) along one side (the sunny side again) in the shallow end each having 3 attachments to the wall (under water). One of these bars has 2 of its attachments that have reddish-brown rust and a stain flowing down an inch or two from the attachment hole and this hole looks metallic, but not stainless steel. My hunch is that this rust occurred a year and a half ago when I was using TriChlor tablets in a floater since the floater was tethered somewhat near that area (though I would push it towards the center of the pool after closing the cover. So my guess is that the acidity from the Tri-Chlor caused the rusting.

However, even though I've been off Tri-Chlor for about a year and a half, it looks like there is still additional rusting occurring although very slowly. My numbers are as follows:

pH 7.4-7.5
TA 110
FC 3 (2-4)
CC 0
CYA 15-20 (hard to tell since < 30, but probably in this range)
CH 260
TDS 700 (estimate)
Volume: 16,000 Gallons (16'x32' but with interior ramp and side seat that take up volume)
Temp. 88ºF
Type: Plaster over gunnite (I think) with tile/grout around the surface edge.

I have an electric opaque pool cover so have little chlorine usage (about 0.5 ppm per day) and virtually no pH drift. I use liquid chlorine (12.5%) and occasionaly Muriatic Acid when needed (which is not often). I have also been on half-doses (i.e. every other week) of clarifier (I have a cartridge filter), enzyme scum removal, polyquat algaecide, and MPS shock, mostly because I get these free from a friend who works for a company that, among other things, makes pool specialty chemicals. I'm thinking of cutting back or eliminating these extras based on this forum (obviously not for economic reasons, but to simplify pool maintenance).

My questions are:
1) How can I remove the small stains on the floor of the pool?
2) Will this also work to remove the much more intense stain at the metal bar attachments?
3) How can I prevent or stop the rusting of the metal bars, assuming they are in fact still rusting?
4) How can I prevent future stains from occurring on the plaster?
5) In case I'm wrong about these being stains, how can I tell for certain that they are not some form of algae?

Thanks in advance for your help.

Richard

[mbar]

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.

[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