MH and Eggcrate

[robchuck]

I am starting up a 29 gallon system and don't want to use a canopy (mainly for heat-related reasons), so I devised and built a housing for a 250W MH that's somewhere between a pendant and a canopy (basically a wooden box on stilts attached to the stand) I'll post some pics later this weekend) that will allow me to run open-top.
I planned to simply lay a sheet of eggcrate across the top of the tank, but now I'm getting worried that the heat from the 250W light 12" above the water might be too much for the eggcrate and melt it.
Does anyone have any experience with eggcrate under MH?

 

[robchuck]

bump

 

[golfish]

RobChuck,
I've had Eggcrate sitting on my tank for a little while (maybe three days) I guess about 7" away from the 400 watt bulbs with no melting...I also have a large fan blowing over the top..
Why don't you just try a small piece and see what happens.

 

[newty]

i recall someone mentioning that the eggcrate melted over a period of time, looking like stalactites. i believe that the bulb was less than 3 inches from the eggcrate.
newty.

 

[iyaoyas]

My MHs are 8 inches away from my eggcrate and I have had no problems at all.

 

[robchuck]

Thanks for the advice everyone!
The canopy is built and sitting over the tank, and I will hopefully have the MH wired up this evening for testing. It looks like the bulb will be about 9" above the eggcrate and 10" above the water.

 

[golfish]

the factor could be fans or no fans

 

[robchuck]

Update: I filled the tank up with freshwater on Thursday for leak testing of the plumbing and I've been running the 250W MH for 10 hours a day over the egg crate since then and can barely even feel the egg crate get warm. I have a 4" electronics fan moving fresh air into the light box and down onto the egg crate and onto the water surface that I feel makes all the difference.
The livestock from my lightly-stocked 65 gets moved into this tank tomorrow evening, and I'll post some pics of the setup and the move in the reef forum either Sunday night or Monday.

 

[fishy411]

A good idea my friend had was to get two pieces of eggcrate and put them around but not under yur MH hes got one piece in front and one piece in back

 

[robchuck]

The eggcrate has been holding up very well under the 250W of MH, but it does block out a lot of light. So, as soon as the tank is acclimated to the light, I plan to cut out a hole in the middle (sort of like fishy411's idea) to allow better light penetration. I'll then have eggcrate that looks like Euro-bracing.
And I'm still waiting to get some pictures of the tank (we packed the digi cam and it still hasn't appeared yet).

 

[crazy4reefs]

i have been trying to figure out how to do exactly what you have done.. i would love to see some pictures when you can. thanks

 

[robchuck]

crazy4reefs,
I'll post some pics as soon as I can. The camera still hasn't surfaced yet.....Urgghh!!!!!
Basically, what I did was build a box out of scrap wood big enough to fit a parabolic MH reflector. Also in the box are two DIY LED moonlights and a 4" fan.
The box has two legs sticking out of the bottom of it that attach to the stand. The stand is about 6 inches deeper than the display tank to allow for a 20g sump. I built a pair of sockets out of 2x4's (they are just three blocks screwed together in a U-shape that outline the perimeter of each leg, with the back of the tank providing the fourth "wall" of support) for the legs to drop into, where they are held in place by friction.
For now, here are some sketches of what I've done:

 

[robchuck]

Front view:

 

[robchuck]

Here is a picture of the sockets, looking down from above. The legs are made up of 2x2 pieces of solid oak and fit snuggly into these sockets. There is very little pressure from the light rig resting up against the tank, and I liken it to LR resting on the back glass (I've done this for years without problems).
The black circles you see in this picture are holes in the top of the stand for drain pipes and return plumbing to route through.

 

[robchuck]

Here is how the eggcrate is currently sitting on the tank looking down from above (the two blobs at the back of the tank are where my return plumbing comes up and over the top of the tank):

 

[robchuck]

And as I mentioned above, the eggcrate cuts out about 20% of the light from the 250W MH, so once the corals are adjusted to this light, I will cut out a section of the middle of the eggcrate to allow for more light penetration:

 

[dskidmore]

I'm not sure I understand the point of eggcrate with a hole in the middle. Wouldn't a jumper be just as likely to get stuck on top of the eggcrate as on the floor?

 

[robchuck]

My thinking was to have at least some eggcrate to keep any potential jumpers in the tank. I'll be taking my chances with the hole in the middle unless I can find something to cover the hole that will let more light through than the eggcrate.

 

[newty]

i believe that someone on this board, i cannot recall who, mentioned that there is a more expensive variety of eggcrate that allows for better light transmission. i believe that it is concaved. so, instead of a conservative figure of 25 percent of the light is blocked, it can be somewhere between 5-10 percent.
i do not know where one can get this, but the local home depot may have it. if not, perhaps ******** design shops?
newty.

 

[robchuck]

Originally posted by crazy4reefs
i have been trying to figure out how to do exactly what you have done.. i would love to see some pictures when you can. thanks
crazy4reefs,
I found my camera, so here are a few pictures: