Metal Stains


May 31, 2011
Buffalo, NY
I moved into a house in the fall almost 5 years ago that has a gunite pool with fiberglass walls. I treated the pool with Baquacil for the first year but with the help of everyone on this form I did a chlorine conversion at the start of the second year. It has worked out great and I'm extremely happy with the BBB method. I have learned a ton about my pool and I learn more every time I come back. Keeping my pool balanced has become quite easy and that has in turn significantly reduced the time needed to keep the pool clean. I'm ready to tackle some of the other more complex issues that have been lingering with the pool.

When I moved in the pool had already been closed. I opened it in the spring and found a large amount of leaves covering the floor in the deep end of the pool. After cleaning up the leaves and water there was a light yellow/brown stain on the plaster where the leaves had been. I didn't do anything with it the first year and it didn't seem to change at all. After finding this forum at the start of year 2 and reading all I could, assumed that it was an organic stain and that keeping the chlorine up and regular scrubbing of the stains that they would clear. No such luck, though, the stain remained and may have become a slightly darker yellow/brown. I also noticed a few other small spots appear in other areas of the pool. They were only about 6" around and a light yellow color. Last year the staining continued to worsen and additional spots and some streaking appeared. At this point the original staining remains (might be a bit darker color than before) and I have many other small - medium sized spots throughout the rest of the pool. The plaster rises about 12" into the fiberglass walls and there is streaking all along the plaster portion of the walls. There are also large streaks along the decline from the shallow end to the deep end and the plaster portion of the deep end walls. There are spots and streaks all over the pool and it makes the otherwise clean pool look dirty. I know it isn't dirty but it certainly looks like it is.

I've read a ton of posts here and since last year I have tried a variety of things to remove the stains. After the chlorine/regular scrubbing didn't work, I tried a chlorine puck on the stains but, as expected, that didn't have an impact. I then tried a Vitamin C tablet and that didn't do anything either. This year, though, I tried the chlorine puck and Vitamin C tablet again and the Vitamin C definitely made a difference. I put the tablet on the stain and within a few minutes the stain began to darken. It didn't quite get black but it was definitely a dark brown/gray. Within about 20 minutes the color dissipated and the plaster looks clean where the tablet dissolved. I tried about 10 more tablets on different stains and all of them did the same thing. Based on that experience I assumed that I dealing with iron stains.

I purchased ascorbic acid and a bunch Proteam Metal Magic in order to do a treatment. In the meantime, I've been reading more and I'm not so sure about the AA treatment anymore. I've now read some posts that have said if a Vitamin C tablet turns a stain dark that it is probably copper instead of iron. If it were iron then it wouldn't get dark like that. I have also read lots of posts that say an AA treatment can make copper staining turn to a darker color with out removing them and that will make the stains look worse.

I don't know where the metal came from but I'm assuming that the metal was in the water when I purchased the house and the previous owner used a sequestrant to keep it from staining. Since I wasn't aware of that I never added any and there is no sequestrant left. Without the sequestrant the metal is free to stain. If it is copper, then I'm guessing that the previous owner either used a copper based algicide or they let the PH get out of balance and copper came from the heat exchange coil. If it is iron, then I'm not sure of the source. My water source doesn't contain any copper/iron.

At this point I'm not really sure how to proceed. Part of me wants to look at the results I got from the Vitamin C tablet and assume that the AA treatment is just a large scale version of that, so I should expect the same results at the larger scale. Another part of me looks at some of these posts about the AA treatment making copper stains worse and I should heed the advise of the experts here and not risk making the stains look worse.

If it is copper and I don't do the AA treatment then I'm only out the cost of the AA. I'll still be able to use the metal magic if I can get the stains lifted. I'm not sure anymore if it is copper, iron, or some mix or both. I also don't know if the type of metal is really relevant since I know that the Vitamin C tablet removed it. I know that in many cases copper staining isn't effected by AA, but obviously the tablet was able to lift the metal staining that I have. If that's the case, wouldn't an AA treatment do the same as the Vitamin C table, just on the scale of the entire pool? I know that I could drain and do an acid wash, but I don't really want to go down that path right now. Maybe at some point in the future but that is a huge hassle and would be quite expensive to refill and re-balance the water.

So what do I do now? Should I go ahead with the AA treatment or is it too risky? Is there something else that I can try to determine the type of metal (if it matters)? I had a copper test come back negative a year ago but it was done at a pool store so I don't know how reliable that was.


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
Key West, FL
I found this post from a few years ago from one of our Special Contributors at the time, Waterbear:
(Perhaps you should try steps 2 and 4 and possibly 5....)

1. hold a vitamin c tablet against the stain (which is underwater--this is important) for about 30 seconds. If ascorbic, citric, or oxalic acid is going to work this will tell you. If there is no change go to next step. If it works do an ascorbic acid treatment.

2. fill an old, white cotton sock with dry acid and tie the top. Fill a small Tupperware container with stones or rocks (we want it to sink and not float) and cover, rubber band the sock to the underside of the container and place on stain (which is under water). Let sit 45 minutes but check at 15 minute intervals. If stain lifts or changes it is not organic and is metal. Proceed to step 4 (sponge test)

3. Take a trichlor tablet, crush it up and put it in a white sock (NOT the one you had the acid in), affix it to the Tupperware container. Brush the stain to disturb any biofilm and place the sock on the stain. Let it sit for 30 minutes. brush well again. If there is any change to the stain it is organic. Organic stains often require quite a bit of scrubbing and an oxidizer to get them off of plastic surfaces. Think of it as a form of mildew (not completely true but there are similarities). You know how hard mildew stains are to remove and they are organic.

4. If step 2 worked the stains are metal and probably copper. The problem is removing them from plastic or fiberglass, which is not easy, since they cannot be acid washed like plaster. Get a bottle of HEDP based metal sequestrant such as Proteam Metal Magic and a cellulose sponge (such as you use to clean the kitchen or bathroom). you will also need your rock filled Tupperware container and rubber bands. Rubber band the sponge to the container and soak the sponge with the sequestrant. Place on the stain. Check in 5 minutes. If the stain lifts and the area under the sponge is back to it's normal color it's metal, go to step 5. If it doesn't resoak the sponge with sequestrant and place on the stain for 15 minutes. If it lifts go to step 5, If it doesn't resoak the sponge and let it sit for 30 minutes. If it lifts go to step 5. IF the area near the sponge turns yellowish at any of these times the stain is organic, go back to step 3 (or use the sodium percarbonate). You WILL need to scrub and use an oxidizer like sodium percarbonate or high chlorine levels (which can bleach a liner--percarbonate is a bit safer but it still can bleach. Think of it like a color safe powdered bleach compared to liquid chlorine bleach that you use in the laundry--it's not but the analogy holds.)

5. Make sure the water level is above the stain line!
If the stain lifted in 5 minutes add one qt. seqestrant per 10k gallons.
If the stain lifted in 15 minutes add two qts. seqestrant per 10k gallons.
If the stain lifted in 30 minutes add four qts. seqestrant per 10k gallons.
Don't try t get away with adding less. It won't work.
The pool will probably get very cloudy for a few days to a week, this is normal. Run the pump and filter 24/7 for about 3-4 days. Check the filter pressure and clean as needed. The pool will eventually clear on it's own. Just let it run it's course. Keep your chlorine levels normal and do not shock while treating and for a few weeks after. This should remove just about all the metal stains.
Good luck...


May 31, 2011
Buffalo, NY
Thanks for the reply! I see that the post you quoted has been quoted a number of times on the forum but I hadn't come across it until now.

Soon after your reply I did step #2 with dry acid in a sock. I expected it to work since the stains also lifted using vitamin c (step #1). As I mentioned previously, though, I'm a bit weary of trying an ascorbic acid treatment since the vitamin c caused the stain to trurn dark before clearing. I placed the sock filled with dry acid on a couple of the stains for about 15 minutes each and it reduced the staining everywhere I put it. It started to lift almost immediately, unlike the vitamin C. After about 15 minutes the staining was significantly reduced. As the acid dissolved in the sock I could see that it flowed slowly with the decline of the pool towards the main drain. It reduced other stains along the path that it flowed. None of the areas had the staining completely lifted but it was quite obvious where I tested it.

I have tried step #3 previously with no effect.

A couple days after this I received the case of Proteam Metal Magic that I had ordered, however, I went on vacation for a week and I didn't want to get into steps #4 and #5 until I returned. I'm back now and the pool tested good so I've taken the next steps. I started step #5 about 12 hours ago by adding 4 quarts of Metal Magic. I didn't see any reaction, after 6-8 hours, though. My expectation was that the pool would at least begin to get a bit cloudy or I would see very minor improvements on some of the light stains. I decided to add 2 more quarts about 4 hours ago to see if anything would happen overnight.

I went out to the pool about an hour ago and there is definitely something going on at this point since the pool has become quite cloudy. It isn't a uniform haze like I expected - cloudy is probably the most accurate way to describe it. The cloudiness appears to be white and I can see it swirling around all over the place near the surface similar to a real cloud. It's dark out so I can't really tell how cloudy it is but I definitely can't see the main drain and I can just make out the seam where the fiberglass wall meets the plaster/gunite floor (about 3 feet down around the entire pool). I can't really see the floor, though, so I can't see if any of the staining has begun to lift. I also seem to remember reading somewhere that the Metal Magic will remove excess calcium until it is reduced to something like 270 ppm. If that's the case then that might be the initial reaction I'm seeing.

I suppose at this point I'm just going to have to wait for it to clear some to know what is going on. Now that I'm reviewing this post again I am seeing that the amount Metal Magic I should add is dependent on the results of step #4. I was under the impression that it was based on how long it took in step #2 to lift the stains. I never did step #4, though, so I'm not sure if I have the appropriate amount of Metal Magic. Since I've already begun step #5 and the pool is too cloudy, it's too late to see how that works. Right now I have added Metal Magic at a rate of a little under three quarts per 10k gallons. Do you think I should top it off to 4 quarts? I don't really want to waste the Metal Magic, but I also don't want to come up short and end up with some staining left behind that might be lifted with four quarts per 10K gallons. Any suggestions?