VHO Lighting Question

[kdfrosty]

I have a 50g reef which I use a 400w 10K MH and 55w x 2 Actinic PC to light.
My issue is temperature fluctuations. During the day I hit as high as 83/84 degrees, and at night I drop to 77/78. 6 degrees fluctuation. My MH sits 8" off of the waters surface in a canopy, and I use two 120mm fans blowing across the MH. My corals are all thriving, but the temp fluctuation is of concern. A chiller is not an option.
So...will VHO's put out near as much heat as the MH that I'm currently using? How will 440w (2x 110w 10K and 2x 110w Actinic) affect my lighting situation?
Note: Im not keeping any clams or SPS corals that would require MH lighting.

 

[chilwil84]

that is a big swing in temperature, have you thought about turning up your heater so at night the temp doesnt fall as low at night. that would be a good drop in light and will probably screw up your coral for a little while but if they are mostly softies and lps then move as many higher as you can and increase the time period the light is on and expect them to not open up the same for a while till thyey adjust, and you should probably increase your heater with the change so you dont let yor daytime temp drop off quickly and slowly adjust it to something like 77-79

 

[kdfrosty]

That's just it...I have my heaters (plural) set to 83. I will try turning them up to 85. It REALLY shouldnt be that warm.
I think that the MH over the tank heats it during the day. It shouldnt be getting as hot as it does, and that's one of the reasons Im considering VHO.

 

[chilwil84]

if you have a fug/sump put a fan blowing across it when your mh are on you should get a degree or 3 of temp drop but even more evaporation if you do change i would look into t5 kits like the icecap retro kit with a 660 ballast they will give more usable light than the vho and less heat than the mh

 

[jlem]

VHO's would be great over a 50 Gallon and 4 110 watt bulbs would look great and would not put out near as much heat.

 

[kdfrosty]

Will I need a reflector of some sort?

 

[bang guy]

Contrary to popular belief the source of the light makes no difference as to how much it heats the tank. It's the amount of light that enters the water, not the temperature of the canopy or the bulbs.
If you have your heaters set to 83F then the temp should not be dropping to below 80F. There's a problem there, maybe you need another heater.
You said that you "use two 120mm fans blowing across the MH". Why are you trying to cool the MH? Isn't it the water you want to cool? Point the fans toward the water if you want to cool the water, not at the MH.

 

[kdfrosty]

The two 120mm fans blow across the the inside of the canopy and top of the tank. I primarily use them in the summertime to increase evaporation thereby keeping the tank a bit cooler.
I also know that it keeps the water temps a bit cooler, albeit just 1 or 2 degrees.
If it's "the amount of light that enters the water" that matters as you say Bang Guy, what do you make of a 400w 10K MH sitting 8 inches above the water over a 50g (48" long) tank? Without a doubt heats the tank.
So, will 440w VHO at 10" above the tank heat it as much as 400w MH 8" over the tank?
One more question:
Ive noticed that a lot of the VHO bulbs have reflectors in them. URI and AquaSun both make this claim. So would I need to use a 48" external reflector as well?

 

[zman1]

I would agree with Bang that the light penetrating water is the primary heat.
IMO ambient heat of a closed canopy which yours is not can transfer heat as well as the ambient room temperature can have an effect.
Unrelated but there have been recommendations of folks to put 60W bulbs in dog houses for outside dogs in the winter and If you live up north they recommend to keep blanket, boots and candle in your car in case you get stranded - heat from a candle can save your life so the news used to say when I lived in MN.
You have been given a few ways to do evap cooling. I would also ask you about the 83 degrees you are setting your heater at, is this just the numbers you're setting the heater knob with? They are not that accurate or is your heater actually on the whole time and not maintaining a higher temp than 78 at night. If it's on all the time then you don't have enough wattage heaters to handle the tank and the ambient room temp at night..

 

[bang guy]

Originally Posted by KDFrosty
So, will 440w VHO at 10" above the tank heat it as much as 400w MH 8" over the tank?
Yep. In my experience it does.
One more question:
Ive noticed that a lot of the VHO bulbs have reflectors in them. URI and AquaSun both make this claim. So would I need to use a 48" external reflector as well?
You wouldn't require a reflector but quite a bit of light escapes the internal reflectors. An external reflector will capture this light and send it into the water. A lot of VHO users paint the inside of the canopy to do this but an actual reflector is better by far.

 

[kdfrosty]

I'm going to have to experiment for a couple of days with the heaters.
As far as the lighting goes, I'll let you know what I decide on.
Thanks for all your help!!

 

[reefraff]

If you are going to switch from halides go with T5's. They can put more light and less heat into a tank than halides, and I have confirmed that with a PAR meter. They probably wont beat 400 watt halides but that is overkill if you arent raising SPS and clams anyway.
If you go with the T5's don't mess with overdriving them, not needed unless your raising clams, SPS and anemones. Just a Tek retro.

 

[bang guy]

Originally Posted by reefraff
If you are going to switch from halides go with T5's. They can put more light and less heat into a tank than halides, and I have confirmed that with a PAR meter.
Can you publish your results? I've been waiting for someone to do an unbiased comparison but so far everyone compares the best T5 combinations with the worst MH combinations.
I'm very interested in your results.