Blue/Purple Stain


Jun 14, 2007
Baltimore, MD
This has not been my year. I have gotten some great advise on here and I am back for a little more. I am using the BBB method and my numbers are as follows:

Free Cl 16ppm
Combined 2ppm
Total Chlorine 18ppm
PH 7.2
Alkalinity 100
CYA 100

My problem is that I have a blue to purple colored stain that goes around the pool at the water level. It comes off of the vinyl liner fairly easy with a little scrubbing. The bigger problem is that it has turned the fiberglass parts (steps, seats) a blue to purple color and it does not want to come off of these parts.

What is causing it, what is it, and what can I use or do to get rid of this?

My thought is that I have some metals in the water and this is causing my problem. They did work on all of the water mains in the neighborhood and I think that I got some metals in the pool when I topped the level off.

I have read the Metal Free bottle and it says that it will remove metals from the water, but what will remove the purple stuff?

Thanks in advance for all of your help


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
What else has been happening recently? I see that you have CC of 2, which suggests some kind of algae or other organics problem. You should shock the pool to get CC down to zero. Did you add any chemicals you don't reguarly add or try a new brand of something recently?

You can test for metals fairly easily. Get some Vitamin C tablets, crush a few of them and put the powder in a sock, rub the sock gently on a stain and see if it changes. If it is metals it will probably disappear in that local area and metals treamtments can be used. If it is not affected it is probably something else.

Having a CYA level of 100 can be problematic. Many of the CYA tests will show levels above 100 as if they were 100, so your level could be much higher. I suggest you replace water to bring CYA down below 100.


Mod Squad
TFP Expert
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In The Industry
Apr 1, 2007
Sebring, Florida
Off topic for just a second. If that 2ppm of CC is correct, that suggests you need to shock the pool.....up to at least 25ppm with your high CYA of 100. That may or may not improve your staining but that needs to be addressed.

Metal is frequently blamed for problematic pool water but it is the cause rather infrequently. The most common metal is iron from well water and it precipitates out onto the surface with brownish/rust stains. Copper is probably next and normally shows up as dark blue or dark bluish/green stains. YOurs is, of course, neither of those colors. I cannot comment on the appearance of manganese stains. However, this quote from waterbear...the testing guru
pink/violet water is often caused by manganese. Try a metal sequesterant and if the water turns back to normal you have your answer (since most pool stores don't test for manganse). Even if you don't need it a dose of metal seqesterant in the water won't hurt anything.
Sound like solid advice to me.

I would bring your FC up to 25-30 and hold it in that range until your CC's test .5ppm or less and your water is clear.

The rest of your numbers are fine.

PS - the metal "removers" don't. They simply return the metals to solution but they're still in your pool. Metals are only removed from pool water by draining and refilling or a water softener.