Should I remove these leaves?

[Chrispowell]

Hi all, seem to get this black algae on older plant leaves..

What is it and how do I fix it?

Also is it better for the plant if I remove any leaves with this on??

Thanks

 

[xim]

I think when you trim the tops, the plants lose the best parts of their food producing organ. So they cannibalise old leaves to survive and feed new buds.

From the look in the photo, either the plants have used them up or they are already being discarded from being too old. I would remove most of them.

 

[ChrisP]

I would trim them back, it will help the rest of the plant to flourish.