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Old 01-19-2006, 12:14 PM   #1
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14,000K MH burning corals

For the past year, I have been running (2) 150w 20,000K MH DE Coralvue on my 72 gal bow reef. I supplement that with 130W 10,000K PC and 130W actinic and use them to create a dusk-to-dawn effect. The MH photoperiod is 10hrs/day. I decided to switch to (2) 150W 14,000K MH DE Phoenix to gain a little more PAR. I acclimated the 14,000K bulbs carefully with screens for a period of 4 weeks. Everything went fine. However, now that the screens have been removed, I can't keep the 14,000K phoenix bulbs on for any longer than about 3hrs/day without burning my corals. The LPS corals are all near the bottom of the tank and I have various species of Acropora, Montipora, and Pocillopora near the top. The MH bulbs are about 8 inches off of the water surface (that is as high as I can get them) which means that the closest corals are within about 15-16 inches from the lights (7 inches below the surface). The Montipora and a few of the Acropora suffer the most. When the lights are on for any longer than about 3-4 hrs/day, they start burning the tops facing the lights. What the heck is going on? How can 150W bulbs be burning Acro? Any suggestions? Am I doing something wrong? Any help or recommendations will be greatly appreciated.
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Old 01-19-2006, 12:32 PM   #2
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I'm gonna give this my best shot and any one here who can add in...please do.

I'm taking a guess and say it may be due to the intensity of heat MH put off. Maybe being 14,000K has something to do with it too. Even though acropora, montipora, table coral, etc. are momentarily exposed to air from low tides during the equinox, they are not getting super intense heat for any considerable length of time. The low tide lasts for what? A few hours at a time? So this would coincide with those lights being ok for only a few hours.

You may want to consider different lights to replace the halide, get a different halide, or get a bigger, deeper tank.

Are the coral on the bottom getting burned too?
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Old 01-19-2006, 05:25 PM   #3
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What are you observing (physical symptoms) as the corals getting "burned"?
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Old 01-19-2006, 09:54 PM   #4
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I keep my temp 80-81 degrees. The tank is in the basement and it's always cool down there so rising temps from the MH are not an issue. The phsical symptoms are lack of polyp extension and whitening of the coral on the branches facing up so it's obviously a reaction to these bulbs. The bottoms of the branches (away from the lights) are just fine. The LPS corals are not having much of a problem since I have them all so deep. Again, the SPS corals are near the top and can't seem to handle the intensity of these bulbs for more than 3-4 hours/day. I could move them deeper but I don't want to do that because I won't have any corals near the top. I have since replaced the 14,000K Phoenix bulbs with the 20,000K CoralVue and everything is fine again. Too bad because those 14,000K bulbs looked awesome. I just can't understand how 150W MH bulbs can burn the corals like that... most people seem to be running 250W bulbs on a tank of this size and don't seem to be having problems. Any other ideas?
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Old 01-19-2006, 11:37 PM   #5
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If acclimated properly seems like it could be a UV issue with the bulb. There were some bulbs last year that ended up having a problem with the UV filter on the bulb. This caused burnt corals.

Just an idea....
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Old 01-20-2006, 08:49 AM   #6
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If acclimated properly seems like it could be a UV issue with the bulb. There were some bulbs last year that ended up having a problem with the UV filter on the bulb. This caused burnt corals.
That's what I've suspected too. It does have a glass UV shield on it (it's an HQI bulb so it comes with a separate glass shield) but the ends remain uncovered. I talked to Jay at Premium Aquatics about that a few weeks ago and he suspects some UV could be leaking out of the uncovered ends. In order for that to happen, the UV radiation would be traveling horizantely to escape out of the UV shield and be getting reflected down into the display tank (assuming that UV light can be reflected like that). Any ideas how I could rig this unit to prevent the UV leaking out? It's a Coralife unit that clips on the back of the tank. I thought about placing a glass shield on the whole bottom to make it impossible for UV to leak out, but then the unit may not be able to cool properly.
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Old 01-20-2006, 11:53 AM   #7
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Indy...you've hit the bullseye. That's exactly what my friend suspected when I asked him. He asked me if they were HQI and he said if so, then most likely it's the UV. These bulbs must be covered completely with a glass shield or they will damage the reef. These bulbs are made to be tucked in glass like that so if it's a well made, trustable company, then you shouldn't have to worry about cooling. What's more worth protecting? A few hundred dollar light or the thousands of dollars invested in your reef???

All you need to do is replace it with a different type of MH.
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Old 01-20-2006, 04:12 PM   #8
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If the tips are getting white, the coral is growing not being burnt.
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Old 01-20-2006, 04:16 PM   #9
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If the entire exposed surface is going white then I'd agree it was being burnt/bleached. If it is just the very tips of the corals then pictures would be worth a thousand words. Some corals grow white at the tips as already suggested.
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Old 01-22-2006, 08:07 AM   #10
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I went to a glass shop and had 1/4" plates cut to fit the fixture. I removed the diffuser and installed the glass so now the entire bottom of the fixture is covered in glass... no UV should be able to escape. The 14,000K bulbs are back-in and I'm acclimating so we'll see what happens. Also, which is a better UV shield-- glass or acrylic?
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