Cobalt stains?

Razorhog

Bronze Supporter
Jun 20, 2013
662
Northeast Arkansas
Each year I get some black marks on my fiberglass pool, which might be cobalt staining. CH is currently 60. Would raising CH help prevent these black spots and even remove the ones that are there already? Installed a SWG last week and FC is holding at 6 with a CYA level of 60. I will try to get pics.
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
16,131
Laughlin, NV
I have no experience with low CH and cobalt stains. My fill water is 250 ppm CH so has never been a concern.

I think fiberglass still has cobalt so the recommendation stands. Though I do not think it needs to be that high. Lets ask @Texas Splash
 
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Razorhog

Bronze Supporter
Jun 20, 2013
662
Northeast Arkansas
That pic is from the side wall, where I see them each year. Have some on the bottom too. It has to be something with how the fiberglass shell is produced. All in all they aren't too bad, it's just that the water is so clear you can see them :)
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I suppose this pool no longer has a warranty? Ever asked the manufacture? Have you ever tried some 600 grit wet/dry paper to one of the spots? There's a morbid curiosity in me to see if they go away with sanding or if it brings them more to the surface.

@JamesW, you ever see this?
 

JamesW

TFP Expert
Mar 2, 2011
13,890
Possibly cobalt stains.

 

Razorhog

Bronze Supporter
Jun 20, 2013
662
Northeast Arkansas
I suppose this pool no longer has a warranty? Ever asked the manufacture? Have you ever tried some 600 grit wet/dry paper to one of the spots? There's a morbid curiosity in me to see if they go away with sanding or if it brings them more to the surface.

@JamesW, you ever see this?
No, I’m second owner and believe the pool is 12 years old. Not sure about sandpaper but now I’m curious too...
 
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