How often should I change my T5 bulbs?

Cody's 120-gallon zoa garden illuminated by an ATI Powermodule T5HO light fixture with Reef Brite XHO Blue LED strips.

"How often should I change my T5 bulbs?" is one of the most frequently asked questions we receive from aquarium hobbyists.

Last week Marine Depot received a terrific bulb replacement guide from ATI North America and they generously gave us permission to re-post it here for your benefit. Thanks, ATI!

Factors that Affect Bulb Life

Photo Period: This is the length of time a bulb is running each day. (For example: A bulb that is run for 12 hours per day should be replaced more often than a bulb that is run for 8 hours per day.)

Heat: Hotter installations typically mean a shorter bulb life. We always recommend the use of fans inside a canopy or other enclosure. Also, make sure that hot air can ventilate/escape somewhere. (Remember, hot air rises. So, some slots in the top of a canopy, or removing the top completely can help a lot.) Also, choosing a fixture with an active cooling system is generally a good idea. Be sure that the bulbs are installed in the proper orientation in the fixture. The end with the label should receive the most cooling.

Ballast: Programmed-start ballasts typically provide better bulb life than instant-start ballasts, as they are easier on the bulb during start-up. We generally do not recommend over-driving any T5 bulb, as it will shorten bulb life by about 50% and produce more heat. Also, over a 6 month period, the bulb will generally produce less total light than a normally-driven bulb.

When to Replace Your T5 Bulbs

Coral Health: If your corals are not opening up as much, or are growing a lot slower than before, it can be a good indication that your bulbs need to be changed.* Soft corals that are reaching towards the light may also indicate the output has diminished and the coral is no longer receiving the amount of light it prefers.

Tank Health: In a mature tank with stable water parameters, algae and/or cyanobacteria bloom can be a good indication that the bulbs are deteriorating and need to be changed.

Time: With typical daily photo periods of 8-12 hours, T5 bulbs carry the average life-span is 9-12 months. If it’s been more than 12 months since your last bulb change, it’s probably time.

* Please note: Immediately after replacing your bulbs, many types of corals may not open up as much as before.

How To Replace Your T5 Bulbs

New bulbs typically produce twice as much PAR (output) as old bulbs. To avoid shock to your corals, it is always best to spread out a bulb change over a period of several weeks. Remember the Reef Tank Golden Rule... Nothing good happens fast.

Change out just 1-2 bulbs per week.
This will allow corals to acclimate more easily to the new, brighter bulbs.

Brand new lamps have a burn-in period of 50 hours. During this time, they should not be dimmed (when using a dimmable fixture). They may also illuminate inconsistently or flicker. Don't worry. This is perfectly normal.

If you keep your bulbs running optimally and replace them regularly, producing beautiful and happy corals will be much easier! If you need some help choosing ATI bulbs for your aquarium, check out this handy reference chart.

Tell us how often you change your T5 bulbs!

Are you running a strict 9-month change schedule? Or do you sometimes run a little longer? We would love to hear about any schedules, as well as any tricks and techniques that you have for your bulb changes in the comments below.