Lighting question: How often should they be replaced?

[fishytime]

Depends on your fixture.....if its actively cooled (meaning fans in the proper places), then probably up to a year....if its not an actively cooled fixture then 6-9 months, depending on use of course. Side note: fiji purps look great but give off alot of the red color spectrum, which tend to help feed algae growth.

[Myka]

I change my T5s around 9 months. They aren't fan-cooled.