When should I change my bulbs?

[megabyte]

I am running 2 165w VHO's a 10,000K Hallide and a actinic light. When is the best time to change them. From looking at the tank everyday it is impossible to tell if they are still as strong as they were when they were new. They must loose there potency at some point.
[ September 10, 2001: Message edited by: megabyte ]
[ September 10, 2001: Message edited by: megabyte ]

 

[captain hook]

I think the rule of thumb is every 6 months, but my local fish guy said he usually stretches it on his tanks to about 8-9 months. I think it probably depends on the light requirements of your corals. I have 4 VHO bulbs on my tank, so I'm taking the approach of replacing 2 at a time and going for about 9 months between replacements. This way I know I have at least 2 fresh bulbs over the tank at any one time. I also think it will keep a more steady light intensity on the tank over time vs replacing them all at once and going from dim to bright over night. JMO.

 

[up north hermit]

It really depends on the type of ballast you use on the VHO's. If you use a tar and coil ballast the life of the bulbs is about 6 months. If you use the newer electronic ballasts, the life of the bulbs is greatly increased, to 12-18 months.
I take a middle road with my VHO bulbs. I have 4 VHO on a icecap 660 electronic ballast. I change one bulb every 3 weeks starting in the 11th month, giving me all new bulbs by the 13th month.
Whatever you do, it is best to stagger the change over, do not do them all at once.
HTH
Hermit

 

[mr . salty]

HERMIT makes a GOOD POINT there...Any sudden change/upgrade in the lighting WILL cause problems...It is a VERY GOOD idea to do it as he suggested...GOOD ANSWER HERMIT

 

[up north hermit]

Hermit

 

[sonny]

I agree with everyone so far. When you change all of the bulbs at once, it increases the intensity a lot, which could be bad for your corals. Metal halides need to be changed every 12-18 months. If you have more than one MH, change one at a time to avoid problems. For VHO's, with the Icecap ballast, 12 months is the recommended time. I think you could eek out a couple of extra months!
Sonny

 

[megabyte]

Thanks for all of the useful info. I am runnung electronic ballasts on my VHO's and Hallide. I use a tar for my actinic. Changing them gradually does make the most sense to me also.