Pinkish hue is developing outside of pond

[rb needs help]

Pinkish color is not slimy. I add sodium hypochlorite 12% each week for the past 2 years and no problems. the demand is high due to the fact of no filtration. When I add sodium hypochlorite directly onto the pinkish hue, it turns black. but doesn't kill it. Pond is made of title on the walls and bottom. any idea's?

 

[MitchM]

Looks like a permanganate stain on marble?
You could try different oxidizers in an inconspicuous area.
Maybe hydrogen peroxide.
If this is municipal water, there should be a test available from your municipality to tell you what's in the water.
If you never do water changes, perhaps you've had a mineral (manganese) buildup over time.

 

[Jhn]

There is also a bacteria that can turn areas a pink color that are constantly wet. Just another thought in case it is not as Mitch suggested.

 

[Lisak1]

There is also a bacteria that can turn areas a pink color that are constantly wet.

I was going to add that - airborne bacteria, common around damp areas. But if it's not slimy and doesn't wipe off then maybe it's staining from your water. I agree with @MitchM - try H2O2.