Need advise on algae...thx

[Jetstream]

Hi everyone...would like to know if the algae that has grown on my hang-on filter is a good one or not? It started out as greenish stuff and over time became dark like in the pic.Should I remove them or leave it as it is?Are these considered bio-filter? Nitrate and CO2 levels within tolerable range. Please advise.Thanks so much.

[barmby]

it LOOks like dirt attaching to it. mould like algae. any close shot will be great.

[tripleJ]

i clean them off once every 2 months. seems pretty okay. i am using a liberty hof as well. think is most likely, algae and sludge.