Purple urchin...how much seaweed?

[Erink]

Hey everyone,

My purple urchin is about 2.5 inches. He seems happy but I'm concerned about his eating. He moves around the tank on the rock, I'm assuming eating. A lot of my rock is white now... I am supplementing with green seaweed. My problem is that I dont know how big of a piece I should give him. I know he'll reject it if he doesn't want it. I just dont want extra seaweed floating around. I've been giving a piece approximately 1"x 1.5". I roll it up.
Thank you for any advice you can give

 

[reef lover]

I would put a half a sheet attached to rubble every few days.

 

[Erink]

Thank you!