MH Light bulb

[Stephen]

I just changed my mh bulb on my fixture a few days ago and now most of my colals are bleaching. Any thoughts? I've never changed a bulb in the past and had such negative reactions from my corals. I did go from a 14k to a 20k bulb, not sure if that makes a difference or not.

[victoly]

how old was the old bulb? PAR in old bulbs drops over time, and if that drop was significant enough, it could cause bleaching. did you do a water change, add carbon or iodine during that time? If you increase water clarity at the same time, you can have a bleaching event.

[FarmerTy]

Rule of thumb I go by is shortening photoperiod when switching to a new bulb and acclimating over a period of 1-2 weeks until returning to full photoperiod.

I do that normally for direct replacement of exact same bulbs. If you are switching spectrum as well, I would give it an even longer acclimation period.

[jestep]

The 20K should be much less intense than the 14K unless the 14 was very poor quality or really old. I would back way down on the lighting schedule. If literally everything is starting to bleach, you may want to go actinic only (assuming you have some) for a few days to a week to let them recover and then slowly start adding the MH back into the photo cycle.

[Stephen]

how old was the old bulb? PAR in old bulbs drops over time, and if that drop was significant enough, it could cause bleaching. did you do a water change, add carbon or iodine during that time? If you increase water clarity at the same time, you can have a bleaching event.

Not sure on the age of this bulb actually, could be quite old since I bought it used. Water quality is okay as far as I know. I did a 50% water change last week when I found out my skimmer was rusting in my sump.. Also, added a poly pad, change my gfo and my carbon. Corals were responding favorably to the water change though

Rule of thumb I go by is shortening photoperiod when switching to a new bulb and acclimating over a period of 1-2 weeks until returning to full photoperiod.

I do that normally for direct replacement of exact same bulbs. If you are switching spectrum as well, I would give it an even longer acclimation period.

I normally run a 10 hour light cycle. Maybe I'll run for 4 or 5 hours tomorrow, I think I might just leave the lights off today. Even the coraline is bleached.

The 20K should be much less intense than the 14K unless the 14 was very poor quality or really old. I would back way down on the lighting schedule. If literally everything is starting to bleach, you may want to go actinic only (assuming you have some) for a few days to a week to let them recover and then slowly start adding the MH back into the photo cycle.

I don't have any actinics, but I think i have a cfl fixture in the garage. Might hook that up and give my corals a break. what do you think?

[FarmerTy]

I'm sure the actinic wouldn't hurt but if it was me, I wouldn't even bother and just start with a day or so of no lights and slowly ramping up from there.

[jestep]

The 20K should be much less intense than the 14K unless the 14 was very poor quality or really old. I would back way down on the lighting schedule. If literally everything is starting to bleach, you may want to go actinic only (assuming you have some) for a few days to a week to let them recover and then slowly start adding the MH back into the photo cycle.

I don't have any actinics, but I think i have a cfl fixture in the garage. Might hook that up and give my corals a break. what do you think?

I would just back way off on the photo period then. Dont add new lights, it would just complicate everything. Since you're already starting to bleach, you sort of need to exagerate it the other direction.

At 10 hours, I might even go down to 2 hours per day and see if the bleaching stops and reverses. A day or two of blackout probably wouldn't hurt at all.