Metal stain that won't go away on plaster


New member
Jul 22, 2007
Hi folks, Looks like a great forum. Thanks in advance for the help.

Pool: Indoor, 13,000, Cartridge, Frogger system (low CL), Heater, I can not bypass the filter and heater.

Chemistry originally: CL .8, PH 8, Adj tot Alk 107, Hardness 200
I've got metal stains (clorine test won't remove; muratic test does remove) that won't come out. Stains are over most of the pool area. Color is blueish-greenish, mostly little light dots. Pool is 12 years old. I had no trouble before but I let the PH get high for a while because I was not paying attention to the pool. Stains appeared then so guess stain is from the heater.

Chemistry before this step: CL 0, PH 7.0, Alk ?
Per the pool dealers instructions at the recommended dose. I tried Bioguard "Stain Remover" (3lbs) in conjunction with "Metal Magnet Plus" (1.3 QT). I followed all instructions, lowered CL to 0, I even left the "Stain Remover" circulate for 3 extra hours before adding the Metal Magnet Plus since the stain was not being removed. Let pump circulate for 2 days. Stains are unchanged.

Chemistry before this step: CL 0, PH 7.0, Alk ?
Then I started reading on the internet and found this group. I saw MBAR's post about ascorbic acid so I tried it. I was not sure if it would work on a plaster pool (since all mentions of ascorbic acid is with fiberglass pools). I also have a cartridge filter so I was not sure if that was a concern. I did the ascorbic at 1/2 lb per 10,000 then later added 1/2 lb per 10,000 more since the stains were not being removed. There is no change in the stains. But I did notice the stains are returning to where I had used a siphon cup to muratic acid some small brown stains. The Muratic originally had completely made the small brown spots disappear and additionally had completely cleared the stains under the sipion cup. But those retruning stains were probably back before the ascorbic treatment and I did not notice.

Could the low (107) alkalinity have caused this not to work?

So the remaining options I know of are:
1) Lower the PH to 6.0, run pump, kind of doing a mild acid wash, don't know if this will hurt filter or heater.
2) Or use sipion cup to apply muratic acid directly stains on the pool bottom (will take a couple of hours)
3) Or drain and acid wash the pool
In cases 1 and 2 I know I need to put in a sequestering agent to hold metals in suspension. Then I would assume a flocculent to catch them in filter.

Thanks for the help - sorry this got so long.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
If stains are returning then either you don't have enough sequesterant in the water or they aren't metal stains. My guess is they are metal stains, but it would be good at this point to be sure. Have you tried lightly rubbing an area with a sock with ascorbic acid powder in it? I would expect the stain to fade away in that local area if it is a metals stain. Muriatic acid is much stronger and will clear several different kinds of stains.

Lowering the PH below 7.0 is a risk to the heater. If only done for a short time it would probably be fine, but I wouldn't want to go there unless you were fairly sure it would work. Hopefully mbar will have some suggestions.


LifeTime Supporter
Apr 24, 2007
Ashland PA
I see you have a frogger system - it intorduces minerals into the water, which can cause staining. I think you may have copper stains. Jack's Magic has a product called Stain Solution #2 for copper stains. I am not familiar with what the chemical is. I know that ascorbic acid is the chemical in Stain Solution#1 for iron. The only problem with the Stain solution #2 is I think you do have to bypass the heater when doing this treatment. Maybe someone else like Waterbear , or Chemgeek will know the MSDS of Stain Solution#2, and can tell you what chemical it is. You can also contact Jack's Magic, they may be able to help you better, as I am more familiar with iron stains. Here is a link about Jack's Magic:

Hope this helps, feel free to ask any other questions you have :)