Rust color growing on my rockwool blocks

[1971]

I have never seen this, but it has been quite some time since I've grown in just rockwool. I'm use to algae forming, but i'm seeing a rust coloring on some of them. Any thoughts?

 

[Legion]

There are many kinds of fungi that will thrive in that condition. Some can be reddish in color or the worst is black..

 

[1971]

gotchya. I covered the tops of the blocks and will then spray with either oxidate or a weak bleach solution.