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- Jun 14, 2016
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Metal halides (when compared to LED lighting) are outdated for the vast majority of reef systems. They consume more energy than LEDs, they don't offer a true day cycle that results in varying PAR being spread throughout the tank, just as it is on a natural reef and you can't adjust spectrum and output on the fly. Also, MH bulbs start off strong, giving off a spectrum closely matching their advertised Kelvin rating, but over-time this deteriorates and both spectrum and output change. For most reefers, the clear choice is LED lighting as it one-ups metal halides in almost every regard.
However for SPS keepers there is a lot of discussion about whether or not LEDs are truly the weapon of choice for growing SPS corals. I shut my SPS only tank down last year, giving some of the colonies and frags to friends and planting some of them in my large mixed reef. I ran metal halides up until closing the tank down and had switched to LED for a year or so, before pulling the halides out of the closet. I can't give a definitive reason why, because I was measuring PAR under both lighting systems and it was comparable - but my SPS corals (mainly acros) just did much better under halides. I found that newly acquired colonies didn't lose coloration nearly as often and didn't take as long to become established and start growing. I've seen similar scenarios with clams as well. My personal theory is that the intensity of halides throughout the day is the culprit. With LEDs, out of a 6-10 hour light schedule, you may get 4-6 hours of actual high intensity PAR. With halides, you get high intensity PAR for the entire duration the lights are running. Just a theory.
However for SPS keepers there is a lot of discussion about whether or not LEDs are truly the weapon of choice for growing SPS corals. I shut my SPS only tank down last year, giving some of the colonies and frags to friends and planting some of them in my large mixed reef. I ran metal halides up until closing the tank down and had switched to LED for a year or so, before pulling the halides out of the closet. I can't give a definitive reason why, because I was measuring PAR under both lighting systems and it was comparable - but my SPS corals (mainly acros) just did much better under halides. I found that newly acquired colonies didn't lose coloration nearly as often and didn't take as long to become established and start growing. I've seen similar scenarios with clams as well. My personal theory is that the intensity of halides throughout the day is the culprit. With LEDs, out of a 6-10 hour light schedule, you may get 4-6 hours of actual high intensity PAR. With halides, you get high intensity PAR for the entire duration the lights are running. Just a theory.