The 6 Month Rule for Lighting


One of the biggest debates in the saltwater tank world is how often light bulbs should be replaced.

Some people say every year, some say not until it burns out, some say every 6 months.

Here is the answer broken down by tank personality:

Tank Dabblers: since you are running fish only tanks (better known as FOWLR): every year

Reef Enthusiasts: Every 6 months

Reef Junkies: Every 6 months

Here’s why:

As bulbs age, they loose their ability to penetrate the water down to our corals (called PAR). Bulbs also experience spectrum shifts as they age and since our corals need certain spectrums to grow, if that spectrum isn’t there then your corals don’t grow, they turn brown, or bleach and eventually die. (Spectrum shifts can also lead to nuisance algae issues)

Could you just wait until your corals tell you that your bulbs are shot? You could, but that’s like saying that you’ll change the oil in your car once it starts running poorly.

And unlike your car, corals take a long time to recover, so you’ll get to enjoy a nice brown tank until their recovery is complete. (Oh, and by then, it will probably time for another bulb change…)

By changing your bulbs every 6 months, you’ll be staying a head of a problem which can take months to recover from.

NOTE: there is one BIG secret that goes along with changing your bulbs every 6 months, and I’ll talk about that tomorrow.

Browse the Store! Questions?

Comments for this article (4)

  • Luis says:

    Is it better to maintain the brand of lights or sometime without regulary frequency change it ?

  • Luis…even if you don’t change brands, the new bulbs might have a different spectrum since they are new. As bulbs get older, they lose their punch and the spectrum shifts. Replacing the bulbs returns the light in your tank to their full power/spectrum and your tank needs time to adjust.

    If you changed brands, then yes, you’d need to also ramp up your photoperiod. I find a brand that I like and one that works for my tank (good color, good coral growth) and I stick with it.

  • Tony says:

    Mark, what do you think about (or have you thought of ) LED lighting? I am considering it… They are costly at first but would pay for themself for their long life. I am just not sure if they are good enogh for corals.

  • Dave says:

    Mark – Your talk about “Bulbs” and changing them every 6 months to a years depending on what type of tank you have. What is your option about LED’s since they last 10 times longer the Bulbs is there effectiveness also longer?

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.