Algae?

[geoffrey]

Hi Gentlemen,

I noticed yesterday a certain algae?? sort of stuff on my filter tubings. They look like grease patches and are black in colour. Are they algae?

[FC]

I have the same but 2 types:
1) black hard stubborn type (like spot algae but black)
2) slimy brown stuff, sometime furry, coating

I am wondering if they are the good guys (good bacterias).