Lighting question: How often should they be replaced?

[Evil Guppy]

I waited about 14 months before changing out my bulbs.

I didnt realize how dull they had become until finally changed them. All of the corals seem to be doing much better now. I'll probably do as others have suggested and will change the white bulbs every 9-10 months and will keep the actinics for 15 months or longer.

On a somewhat related note, what is everyone doing with their old T5's. Are there any places that we can take them for recycling?