How often do you change your t5 bubls?

[bpro32]

I'm trying to justify a lighting upgrade from 64w pc in the aquapod hood to 96w t5 ho. It's the nova exteme 4x24w. I know it has a single reflector but it is still a huge upgrade. A local reefer is selling his for $90 and its only 6 months old.

 

[funkysean5]

I usually change them every 18 months.

 

[goinbroke]

i've had my t5ho's for a year now. my unit has 4 10,000k's and 4 actinic. 54watts per bulb.
i just changed them and WOW, what a diffrance! i think they should be changed every 6 months. it was a night and day diffrance between the year old bulbs and the new ones!