Hurray for MH!!!

[Sara]

Well, some bug hit me this morning and out of the blue I decided to upgrade to MH! Yea! I'm so excited. I didn't even really care about the money, is that bad? So, here is what we'll have. 1 250w 14,000k MH w/6 lunar lights. It'll be quite a step up from pc. How far should I suspend it above the tank?

 

[Bifferwine]

Start it about 18 inches off the tank, then lower it each day until you see it start to heat up the tank. You don't want it so low that water can splash onto it, though.

 

[Altohombre]

you should have made the bug make you buy a Solaris lighting unit.

 

[fatman]

Does the fixture have a glass or plastic cover over the bulb. The higher the fixture is above the tank the lower the thermal energy (heat) that is transferred to the tank, but the less light that will enter the tank. With the typical reflector at 7 inches above the tank (according to Joshi and Riddle) about 70 percent of the light makes it to the tank. The rest goes into the room or is lost due to it being converted to heat when not reflecting entirely from the reflector. Higher than that and even less of the light will enter the tank. That much wattage might be a heat problem with a tank as small as 29 gallons. Do you have a sump hooked up to the tank? At the least a fan or two will be needed to provide additional evaporative heat loss. Your tank will not lose enough heat through the tank walls alone to provide cooling for the heat that the halide light will add to your tank. Having the light much further than 9 inches or so kind of defeats the purpose of having halide lighting. My halides on my tanks are five inches above the rim of my tanks. Which means 6 inches off the waters surface. However I keep my room temperature at 68 degrees. I have 3.5 gallons of evaporation per day in a system with a 120 gallon tank and a 40 gallon sump. Combined water is around 120 gallons due to deep sand bed, live rock and free space at top of sump tank for drain down when the power goes out. There are two 250 watt halides, two 96 watt PC's and only two 4 inch box fans over the sump. I actually lose heat during the period of time when all lights are on, but I run tnk temperatures of around 80 to 82 degrees in a 68 degree room.

 

[Sara]

The fixture does have glass over it. I have been worried about heat, especially after last summer. I will be purchasing fans for the waters surface. I don't have a sump, I thought it pointless for such a small set up. I guess if the 250w ends up giving me and the coral an extra tan then I'll move it down to a 175w.

 

[fatman]

A 15O watt HQI is more commonly used with a tank that size, especially when there is no sump to increse the water mass and to provide for water evaporation. However with a glass lid you will have less light entering tank (and therefore less heat) as some will be blocked and some reflected by the glass cover. Most reef tanks do not utilize glass tops beacuse of the cooling effect of not having a cover and the increased breathing (giving up carbon dioxide and taking on oxygen) ability of the tank. Without a fan cooling the glass some of the heat will be taken up by the tanks air and transferred to the water. However a good deal will be given up to the room air. You do not mention if your light fixtyure came with a cooling fan. These help a lot. A computer box fan would probably provide ample air circulation between the light and the tanks glass cover. I woud still put the light pretty close to the top of the tank. Something like 5 to 8 inches. If the heat becomes a problem a fan at some distance from tank pointed at the tank will create a constant air movement around tank causing increased heat to flow through tank glass therefore cooling tank.

 

[Sara]

The glass top will be off of my tank. It has been for a while now. I'm just lazy about topping off. My light fixture will have cooling fans. Also, I will place an oscillating fan next to the tank in the summer to help out more. I am also planing on buying a little fan to attach to the tank for more air. I think I'll be okay. They arrive tomorrow!

 

[fatman]

The greatest amount of heat removal you can provide is through water evaporation. A small fan attached to the tank blowing air across the water surface will probably handle the job. The oscilating fan will also help a lot, but less than the water evaporation. Moist air carries much more heat energy than dry air.