The bulbs usually need to be replaced at the 8-12 month mark. Your instructions that came with the unit will usually tell you. Some Simply burn our during that time, some just become so weak that they are basically doing nothing.
I run mine 4 hours a day. To help with free floating algae because the room is bright during the afternoon. I have a coralife and bulbs need to be replaced every 6 months
Until I see algae I guess..
