dont have one personally but try algea sheets or seaweed sheets and use your cleaning magnet to keep it in place and the lmb will graze off of that or you can feed a veggy based formula food.
They are constantly grazing on algae. I supplement with nori but, that does not take the place of their need to chomp on algae all day. LMB's can slowly starve to death without enough algae. Mine is about 4 inches and will probably get to about 5. HTH
Mine keeps grazing on the glass and rocks all day for algae and I have plenty of it. I've had him for a while now and he is doing fine.(wish I'd kept records of date purchaesd for each fish) I don't think you can run out of algae cause it will grow back. Just don't scrape the back and side off. HTH
I don't know if others peoples' do this as well but mine also readily eats the mix of fish food I feed my other fish. I've had mine a little more than a year now.