Black residue on thermometer

[Chaddy]

FC - 1.5
CC - 0
PH - 7.6
TA - 60
CH - 360
CYA - 30
Borates - 50-80

I have been accumulating a black residue that feels a bit like old adhesive on the top of my thermometer, which invariably ends up in one of my skimmers so that water is always flowing over it. I am pretty sure it is not adhesive as I have cleaned this off several times now. Pool water is crystal clear. Any thoughts? Picture is attached.

 

[pwrstrk]

What I see from your test results is your FC is out of range for your CYA level.

You should be at a target of 4 and never below 2.
pool-school/chlorine_cya_chart_shock

 

[Chaddy]

OK. Do you have any idea what the black stuff is?

 

[Charlie_R]

What do you use to clean it off? As in dish soap or other solvent.

It looks like some sort of industrial grime, possibly oil by-products that are collecting on your water surface.

Any sort of oily sheen to your water surface?

 

[Chaddy]

Charlie - It definitely comes off with soap and water, but this morning I just wiped it off with a dry paper towel. It does act like a petroleum product when wiping it off, sort of like trying to wipe away old adhesive after you've removed a sticker. Come to think of it, I was just doing some trimming with a gas trimmer last night. I wonder if it could be the exhaust settling onto the pool? I did not notice an oily sheen, but then I did not look closely. Thanks for the idea. - Chad

 

[pwrstrk]

Was the trimmer smoking bad like too much oil in the mix ?

 

[Chaddy]

No, not really. In fact I don't notice any smoke at all. Of course there is the smell of exhaust. It may not be the source, but I will pay closer attention to when I mow and trim and when I see this black stuff.

 

[pwrstrk]

Do you think it could be sunblock ? Just throwing things out there.

Maybe try one if those scum balls.

 

[Chaddy]

I have no reason to say it couldn't be. Sometimes that spray-on sunblock does get a little sticky.

 

[JamesW]

This is common in high use pools. People introduce a variety of contaminants that don't break down easily and create oily residue. Sunblock, cosmetics, body oil, hair products, lotion, etc.

 

[easttn]

The black grease in the skimmer is not just common in high use pools. My pool has only been used about 3 times this year and I cant keep the grease out of the skimmer. I dont even worry about it much anymore as long as I sop out the layer of oil on top of the water in the skimmer. My lawnmower burns a little oil but its not noticeable most the time and I was thinking it could be coming from that about a week or two ago. There is always some grass clippings that get blown into the pool, so it is pretty possible the wind will blow some exhaust gas or oil down on to the surface of the water. If you get to looking at the layer of oil on top of the water in the skimmer, it would not take much oil to be trapped there and create the oily residue. I have a two speed pump and the oil does not flush down the toilet so to speak with it on low. Not sure about high speed.