Metal Halide Broke & Coral Died

[denverjon]

So I initially posted my issues under the tank emergency thread but now that I've (hopefully) got the issue under control, I'm posting it here in the hopes of understanding what the heck happened. On Monday, the outer casing on one of my metal halides broke and fell into my tank (as luck would have it, I had taken the glass cover off the fixture over the weekend to clean it and had not yet put it back on). I immediately removed all the glass from the tank while the light actually continued to work for a few hours before I turned it off. Most of my sps that were directly under the light immediately lost their color and polyp extension and I actually ended up losing a couple colonies that were the highest up closest to the light. A number of them still aren't happy but I'm hoping they'll recover. I also lost a borbonius anthias.

I'm trying to understand why the corals reacted the way they did. Was it because the mh glass provided protection from the harmful uv rays and the corals went into shock? And why would it kill one of my anthias, which I've had for a few years and was very healthy up until that point? Interestingly enough, all of my sps that are on the other side of my tank didn't show any negative affects at all and their color and polyp extension hasn't changed.

 

[naterealbig]

The outer casing of a single ended metal halide bulb acts as a UV C filter.

On a double ended halide bulb, the outer casing will not filter the UV C rays, so the fixture glass between the bulb and the tank is required to prevent harmful UV C rays from reaching the animals.

Either way, if the fixture glass was removed, and the casing of the bulb broke, the corals were exposed to these UV C rays during the period the light was broken and on.

This would explain the coral mortality, noting the corals closest to the exposed element died, and the ones further away were effected less. Not certain about the Anthias.

 

[denverjon]

Thanks for the feedback. That all makes sense to me, it was the anthias death that threw me for a loop. I hadn't lost a fish in a couple of years until this so it made me wonder if maybe some chemical got into the tank when the glass broke. I wouldn't think that a fish being exposed to uv rays would be fatal but maybe I'm wrong...

 

[naterealbig]

I wouldn't think so either. I thought that chemical were only found inside the arc tube (metals, salts), but I'm not certain.

 

[alton]

https://www.reef2rainforest.com/2005/12/01/coral-magazine-table-of-contents-dec-2005jan-2006/
See if you can find this issue of Coral magazine

 

[Crabs McJones]

The outer casing of a single ended metal halide bulb acts as a UV C filter.

On a double ended halide bulb, the outer casing will not filter the UV C rays, so the fixture glass between the bulb and the tank is required to prevent harmful UV C rays from reaching the animals.

Either way, if the fixture glass was removed, and the casing of the bulb broke, the corals were exposed to these UV C rays during the period the light was broken and on.

This would explain the coral mortality, noting the corals closest to the exposed element died, and the ones further away were effected less. Not certain about the Anthias.

 

[naterealbig]

[emoji4]

 

[ZoWhat]

Outer glass to a MH is tempered glass....at least it should be. Any breaking of tempered glass should shatter into beads of glass. If you outer casing broke into sharp pieces, it wasnt tempered.

And yes that glass filters out any nm-wavelengths in the UVB and UVC range. Definitely filters out UVC In the 254nm range which will burn anything, even human skin.

Summer sunburns people get is an over exposure to UVC from the sun.

It would help for you to send PICS of the broken glass

 

[JDtimk]

Wonder if the anthias ate some of the glass shards?