A Case of the Pool Measles

Hi all,

Long time reader first time poster, a friend turned me onto this forum 2 years ago. Since then I have been using the advice I learned here along with the PS233 to maintain a gorgeous pool. So what's the problem?

My pool looks like it has a case of the measles, little black measles, scattered across the entire underwater surface. Along with the measles the pool surface below the water has a slight brownish hue.

I tried to remove a few of these spots so I could determine the root cause, PH reducer, vitamin C, finger nail scrapping and even a scotch pad. The spots won’t budge. I am not sure what to try next. It almost seems like the spots are coming from underneath the gel coat. (I certainly hope that is not the case as any solution for that sounds prohibitively expensive.) I hope someone here can let me know what to try next. Below is the history and specs of the pool since I have owned it:

19000 gallon fiberglass pool with sand filter

Chemicals used for normal water conditioning as needed: Clorox Ultra, 20 Mule Team Borax, Baking Soda

FC 8
CC 0
pH 7.5
Alk 120
Cal 170
Cya 60
Coppper .5ppm (tested at pool store)
Iron Not Run (tested at pool store)

Year 1: No spots. Used 3” tabs for chlorination and 5 in 1 shock powder from Wal-Mart. Some minor green algae problems. (Nothing special added to address the algae.)

Year 2 (Learned about this forum): A few spots at end of year. CYA level was 130, stopped using pucks, switched to bleach. Kept Chlorine levels in the 8 – 15 ppm range due to high CYA.

Year 3 (Current year): Spots spreading. CYA level finally lowered to 60, still not using pucks. Even though this is a fiberglass pool I thought I would raise the Cal level just to see if it would help the spots. Usually Cal was 50-70 now raised to 170. (I know it doesn’t make sense but heck nothing else was touching the spots and by the way it didn’t help with the spots but I swear the water is even clearer now.)

Thanks,

Steve

From your description this could be cobalt....only seems to happen to fiberglass pools from what I understand. I will have to do a bit of research and see what I can find out about it. From my understanding oxalic acid is the most effective treatment for this. United chemicals has an oxalic acid product designed for colbat staining in fiberglass pools. Have never used it so I can't tell you how well it works. There is some data that may indicate low calcium levels might be a contributing cause of the cobalt staining but nothing conclusive that I have been able to find.

Quote:

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Originally Posted by waterbear

From your description this could be cobalt....only seems to happen to fiberglass pools from what I understand.

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I believe you are right. It seems to be the only alternative left. I did some poking around on the web and found two products that deal with Cobalt staining; "Cobalt Cure" (United Chemical) and "Jack's Magic". The United Chemical has a better feel to it so I guess I will give it a try. The process is very similair to the advice in the "Brown stains spreading" thread. I wonder what the main ingredient is in Cobalt Cure?

Best,

Steve

Cobalt cure is oxalic acid. I checked the MSDS. Jack's Magic just says proprietary mixture in the MSDS but the same product is used for iron stains also so I will bet it is also oxalic acid since that also works on iron.