New stain on pool liner

Canucklehead

Gold Supporter
Aug 1, 2019
68
SW British Columbia
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
Hello everyone.
A new problem, noticed only today after several days of leaving the solar cover off. 20 or more of these black, comet-shaped marks, ranging from an inch to 4-5 inches in size, in one corner of the poll's shallow end. They do not vacuum off, and they do not brush away!
Please, someone tell me what is happening, and what can I do about it. I hope the jpeg makes it clear what's going on.
Thank you!
 

Canucklehead

Gold Supporter
Aug 1, 2019
68
SW British Columbia
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
Uh, the jpeg doesn't seem to attach. Do I need to use a different file format? I tried a PNG, but it was too large for the server to handle.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,310
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
The forum's server host is having difficulties with attachments. Seems like some folks are able to get them through but it is not consistent. So might want to wait until tomorrow and try again.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,310
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Did you fertilize the lawn in the last couple days?
 

Canucklehead

Gold Supporter
Aug 1, 2019
68
SW British Columbia
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
No fertilizer, but good thought. I did use lime on the lawn 2 days ago, so the timing fits. But it was deployed on the opposite side of the pool...
Could lime - CaO - do this?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,310
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
It would create very high pH in an isolated area and if you have any iron in the water, it would come out of solution.

Take some vitamin C tablets, put them in a thin sock, crush them a bit, and set on the stains. If they disappear, it is iron.
 

YippeeSkippy

Mod Squad
Gold Supporter
LifeTime Supporter
Jan 17, 2012
17,612
Evans, Georgia
Any oak trees over the pool? We have had tannin stains before from tree debris. A little higher on the FC helps remove ours.
 
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