Black Hairy/Slimy Stuff

[ferlew]

Got a tiny water feature in my back garden. A sumo, a green slate monolith with hole drilled through, and various green slate 'rocks', supposed to look like a mini landslide.
Two weeks ago I cleaned out the sump completely and cleaned the little filter, topped up with clean water, and started it again.
Now I notice the monolith (about 18" high, is completely black with a sort of slimy hairy deposit.
Any ideas on what it is, and what I can do to stop it?
Thamks.

[ferlew]

Sump, not sumo.

[rowanwitch]

Any chance of a photo, a stachybotrys might be the culprit

[alavahalf]

It's probably manganese which is an alagae. If your water feature is in full sun, this won't help matters. Put some Hydrogen peroxide in your sump and that should get rid of it.

[rowanwitch]

Manganese is a chemical element have you been auto corrected

[calmck]

I put a bit of bleach in mine

[alavahalf]

It may be a chemical element as you know it Rowan but .. Manganese is a naturally occurring metal that can be found in different types of rocks, soils, and sediments. It typically occurs in lakes, rivers, and underground water supplies. The black slime that accumulates on spouts is bacteria that feed on oxidized iron and manganese in the water.

[ferlew]

Damn, can't take a pic, just been out and hosed it off.
Yes, it is in sun most of the day, had it almost 20 years, it hasn't done it before. My bird bath always has a dark red deposit after the water has dried up too.
I'll google the stachy thing Rowan mentioned, and I'll also try and get some h.peroxide from chemist. Thank you.