MH lighting distance to water surface (1 Viewer)

[dbrock12]

I am getting ready to build my canopy for my 180 gal project, and wanted to know what everyone thought the distance should be for my 250 watt MH single ended bulbs from the water surface. I was thinking 9-10 in. with fans blowing across the water between the bulbs and the water surface. Any suggestions would be welcome.

Thanks
Don

 

[aqua-nut]

I'm investigating the same thing, and I've been told that 10 inches is the minimum, 12 to 14 is better. Someone with more experience should chime in though as I'm planning my own lighting upgrade to MH.

 

[dbrock12]

lighting distance

Yea, I have read distances ranging from 5in to 14in, so their is a wide range of opinions. Just wanted to know if anyone if anyone had experience with what they would consider an ideal distance before I started on my canopy.

 

[Guest]

How do you plan to cool the MH. I have an idea that I am hoping someone will try. iceprobe is trying to use a peltier chip to cool the water in an aquarium will limited success. The reason I believe is that peltiers were designed to move heat from a HIGH heat area to a much LOWER heat area. The difference between water temp and air temp is just not that great (usually no more than 6-12 degrees) The peltier I use to chill O/C'd CPU's is moving heat quite effectively from a 95+ degree CPU heat source to a 74 degree (the larger the difference the more effecient the transfer). From what I understand the temp of the reflector is even higher that 95 degrees possibly topping 100 degrees. Thart would give nearly a 30 degree differential to most rooms.

Here is what I think might work

Using thermal epoxy connect the peltier directly to the outside of the reflector (might be better to use several smaller chips spaced out than 1 large central chip)

again using thermal epoxy connect a heatsink and fan to each peltier.

use an old/cheap computer power supply to provide 250+ watts of metered steady 12V to the peltier and fans. Any left over power could run additional fans, moonlights or any other 5 or 12V gear you might have in tank/canopy/sump

canopy would need to be designed to allow free air flow around heatsink and fan that I assume would sick out the back of the canopy. The better the airflow the better the heat transfer.

my idea was to leave the computer power supply in the computer case and paint the case to match the stand this way it does not look too out of place. I imagine, but have not factored that there would be plenty room inside the case to house ballasts, power strips, UPS, timers, etc to clean up the general area around the tank. Ther should be plenty excess power to run a few case fans to keep all this cool and standard conduit could be used to route power to the canopy and sump to keep things looking neat.

Since I am not setting up the 75G I will not be able to try out this idea right away, but if someone else is willing to give it a try I might be able to come up with some of the parts

 

[Guest]

I have an oceanic canopy. When I lift the glass covers over the tank, they just clear my reflectors. I would guess that the center of the bulb is about 6-8 inches above the glass which makes them a maximum of 9 inches above the water.

 

[dbrock12]

MH cooling

Highestbid:
Sent PM

 

[Guest]

BillD I would not run glass tops on a reef. You are not allowing evaporation and gas exchange. And your lowering the amount of light that will penetrate the waters surface. And if the covers get any salt spray on the covers you losing even more light. Now on the flip side, if your bulbs have to protective glass between them ang the water, you run the chance of water splash and bulb explosion. I would use a piece of glass near the bulb to protect the bulb.

FYI I have two 400 watt halide enclosed fixtures that hang over my tank. And they are both about 12 inches above surface. Heat is an issue, but I cool the room with a.c. and it helps tremendously. I leave the vent open in that room, and close most around the house a little bit to give that room more cold air than the rest, run and open top, and have alot of surface water open (Tank open, sump open, and fuge open topped. )

 

[Trey]

The bigest issue with heat transfer to the water in our aqariums is not from convective heat transfer from the air in the canopy to the water, but rather from radiant heat transfer directly from the bulbs. Besides chillers the most common way to manage this heat is by regulating the amount of power (yeah right, give me bigger lights please) or by fans in the canopy. The fans greatest benefit is not cooling the lights but rather to evaporate a bit of water. Evaporating water removes a huge amount of heat from our tanks. If the rate of evaporation if too great, than the best shot is to either reduce the lighting wattage or to add a chiller.

As for thermoelectric coolers, they are available commercially, but they only give a small amount of heat removal and are, therefore, typically only used on nano's.

I just finished by 180 gallon hood and lighting if you are interested in coming by to take a look before you dive in to yours. Just drop me a PM.

Later,
Trey