black spots on pool bottom and sides.

Paul J

New member
Jul 4, 2010

Just converted to a SWG a couple of months ago.

I have a pop up pool cleaner system and around the pop ups there are black/gray streaks around each one. I have had these streaks for awhile but are getting worse. There are also the same streaks on the wall under side jets. These streaks are now getting a few feet away from the jets along now with few yellow spots on pool bottom 1 by 3 inches but water is crystal clear.

I have the water tested several times for metal and other stains but can't identify stains. I've added chemicals well over 100 the past month advice of Pinch A Penny but stains are getting worse. Was going to try to find a pool doctor but found your web site.

Added treatment to remove phosphates, added algaecides, Had Water tested July 3rd again at another P A penny
FREE CHLORINE 10.0 (Turned SWG down to one.)

Was told I had to shock water weekly even i f fc was normal. PH 7.6, total alkalinity 100, ca hardness 375, stabilizer 60, tds 5k, salt 3700. Does anyone have any ideas? Thanks, Paul J

Pool is 10k gal aggregate/gunite, cartridge filter, circupool 30k SWG. I live in Orlando, Fl and am on well water that is on a water softner/filter/chlorine system.


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
SWSuburban Chicago, IL
A properly maintained pool rarely, if ever requires shocking. Certainly not weekly. This assumes you have your own test kit, one of the ones we recommend, and are diligent about maintaining the proper FC levels. You should order your own test kit, so you don't have to rely on pool store testing which is often innacurate. Plus, you avoid their poor advice, to shock weekly, add algaecide, add phosphate remover, etc. which is usually unnecessary.

To test stains - for metal, use a plain old vitamin c tablet, and place it on the spots. Iron stains will fade immediately. To test for organic staining, place a trichlor tablet on the spots. If they are organic, the tablet will make them fade. If the stains are metal, the pool store testing won't detect metals in the water because they have deposited on the surface of the pool.

Paul J

New member
Jul 4, 2010
I've tried all sugestions above but stains(grayish/black)are continuing to get larger. Trichlor tablets and vitamin C tabs resulted in no change in color of these stains. Water is balanced but have no idea what to do next. Pool is solar heated and temp stays beteen 88 to 90 degrees. Pool is ten years old. I do apprecite your suggestions. Thanks, Paul

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