When to replace bulbs

[chromis]

Really quick question: How often should NO bulbs be changed? I am attributing my cyano outbreak in my 10 gallon to an old bulb (10 months)

THanks
Andrew

[icemark]

Been my experience that it really depends on the bulb and ballast.

Usable life defined as less than a 50% output loss from new.

Most T12 bulbs

Most tar ballasts: 6 months.
Electronic ballast: maybe up to a year if you are lucky (not including the IceCaps)

Most T8 bulbs add two or three months.

[chromis]

It is just a standard AGA 19 watt striplight. I guess I will change the bulb