Too much light - Burning my corals

[Sculpin]

I recently set up a 180g cube that's 4' wide, 3' long, and 2' deep. For lighting I have two 400w MH lights in the center, and a pair of T5s (48") on either side. The final design is supposed to have an additional pair of 48" T5s to go on either side of the MH lights, but I'm still using some T5s in my old tank and haven't moved them over yet.

I've been trying to slowly acclimate my corals to the light by putting down 4 layers of window screen material and removing a layer every week. I just removed the third layer on Monday evening (so just 1 layer left) and a couple of my frags were bright white when I got home Tuesday evening. When I got home tonight, a third frag was dead.

From the picture you will notice that some of the rocks are stacked very high in the tank. I marked the dead corals in red, and as you can see, they are at three different levels in the tank with varying amounts of light.

I remembered a dial on the MH lights that were marked for 400HQI/400w/250HQI/250w. The knob was on 400w, and when I turned it down to 250HQI the light dimmed a bit in the tank.

Questions:
1) Do I need to be slower about acclimating the corals, or if this is just too much light for the corals?
2) Should I lower the amount of light in my tank, and can I safely do this with my current system by dialing the MH lights down to 250HQI or 250w? Any risk of damaging the bulb or reducing the life significantly?
3) Do I need to lower my rock work? Is that high point in the center too close to the MH lights?


Thanks for the help!

 

[mojoreef]

Thats a tough question to answer Sculpin with out being their to see or to take a reading on the par your dealing with. I cant really see the corals so can you tell me what they did?? did you just wake up and they were white? did you have rtn? did it strat on the tips or was it tissue coming off from below??

Mojo

 

[donrando]

yes, I would acclimate your corals to the tank's lighting slower, it can take weeks to months for some corals to get accustomed to new/different lighting, especially if it is high intensity halide lighting.

 

[Sculpin]

Thanks for the feedback Mojo - Since I don't own a par sensor, I was thinking/hoping that a 400w MH light above a 2 foot deep tank (with rockwork 2/3rds up the tank) might jump out as overkill, or seem well within the safe range and I simply need to go much slower acclimating my corals. My big concern is that every layer of screen material I remove is producing exponentially larger jumps in light (instead of producing a smooth and gradual increase), so when I take off this last layer, even if I wait a month to do it, I risk burning 1/2 my corals. I've only ever run T5s so this is my first experience with MH.

As far as how the corals died, the lights turn on at noon and I don't get home until 6 p.m., and both days I came home to totally white/dead corals. After the first day I inspected all my remaining corals for stress or bleaching and they all looked healthy, so I was surprised when a 3rd coral died the next day. I'm also surprised about the locations of the dead corals. I would have expected more of the corals at the highest points in the tank to show stress or die, but that hasn't been the case.

What I'm particularly interested in is the possibility of dialing down my MH lights to a lower setting. Anyone know if this is something these lights were designed to do? I currently have 400w blubs, so would I need to install different blubs (e.g. 250w) to run at a lower setting?

 

[mojoreef]

I dont think you can turn them down buddy, they need that power just to fire normally. On the corals it sounds like zoox bail, which is cause by the coral producing to much oxygen through photo, kind like putting a super oxygen radicle right in the tissue, so the coral releases a enzyme that cause s the zoox to bail. I have done light acclimation exactly like you are doing so it works, just a matter of time. What has to happen is that the coral needs to find it right amount of zoox population for the light it is under, if its loaded with zoox coming from lesser light then when it gets a bunch more the zoox continues producing and overwhelms, so what you are and have to do is to allow the corals to lower their zoox pop.s and then go with the full strength. Not sure if I explained that well or made it more muddy, but that is what is happening .

So go back the the multiple layers and the take a slower approach on how and when you remove them.

Mojo

 

[Sculpin]

Thanks Mojo!

As far as going slower, I currently have my lights on from noon to 10 p.m. Would it help if they were on for less time immediately after removing a layer, or if the lights cycled on and off throughout the day (e.g. 1 hr on, one off) to allow the corals to ease in?

 

[mojoreef]

Yea you can reduce your lighting period and then reduce it further when removing, but I think the more important thing would be time between removing screens

Mojo

 

[Sculpin]

One assumption I made after the first day was that every coral that lived through the first day was in the clear, and then the 3rd coral died.

When I left this morning I had the MH lights "dimmed" to 250 HQI setting. Would you recommend turning the lights back up to their recommended power and putting an extra layer of screen on a little longer?

 

[sandswhitson]

You will burn out that 400W bulb if you keep running it at the 250W setting. I think you just need to acclimate to the ligths better. We have a 75 gallon tank with two 400W MH over it and the corals are doing fine.

 

[Sculpin]

Thanks Sandswhitson. That's what I was afraid of. Also great to know you have no problem with 400w over a 75g.