[bigteddyp84]

When do you know when you need to change a bulb? I have two 150 watts and one is clearly less bright than the other does this mean I need a change?

[RyanG]

How old are the bulbs? Usually you change MH bulbs every 6-12 months

[Krazy]

Originally Posted by reefbuilders

How old are the bulbs? Usually you change MH bulbs every 6-12 months

I'd agree with all of this, but I'd say to change them every 6-8 months, once the color starts to change, that is a dead giveaway regardless of time used.

[MarineManiac]

i've had no problem going 12-18months on a bulb. it all depends on your photoperiod and what bulbs your using. higher kalvin bulbs will need to be replaced more often as there spectrum shifts.