Cleaning coralline off of BioCube sump intakes

[Hoosier]

I've got a BioCube 29.  Coralline algae are growing on the bottom intake for the sump (but not the top).  Does anyone have any tips or tricks for cleaning this off?  I'm worried that if I just let it go, it'll eventually restrict the flow.  Using an algae pad was not particularly effective, and I think a razor blade would gouge the plastic.  And I obviously can't just soak it in citric acid, the way I would a powerhead.

 

--Hoosier