need final advice on MH....

[marinefish]

ok, i have narrow it down to either the 175 watt metal halide or the 250 watt metal halide. either choice i go with will have color temp of 10K. the price difference between the two metal halides is a difference of $16.00
The metal halide is for a 20 gallon tank. This metal halide will be mounted about 8-10 inches off the surface of the water in a cannopy. Cooling will be provided by two of the table top clip on miniture fans which will turn on as the lights are turned on and off as the lights goes off.
This 20 gallon reef tank will have sps corals, corcea clams, maxima clams and all kinds of other corals both with high light and low light needs. the tank is about 18 inches high (top to bottom), 20 inches wide (from left to right), and 10 inches in width (from front of the tank to back of the tank).
My question is, with my tank size and the kind of corals i want to keep, is 175 watt way enough for my tank or is 250 watt better for my tank? also will the two fans i am planning to use for cooling, will i still have temperature issues? please reply asap, need to make the purchase soon.

 

[sebae0]

for 16.00 dollars difference i'd get the 250w, and if you upgrade your tank at any point it will be better for a larger tank than the 175w.jmo good luck

 

[bang guy]

175 is my vote but Sebae has a good point about upgrading. There is a much greater variety of bulbs in the 250 watt size too.

 

[broomer5]

MarineFish
Have you considered a hanging pendant type of MH fixture ?
I think you'll have some heat issues using either MH in a canopy over a 20 gallon tank.
I may be mistaken though.

 

[marinefish]

i did take that into consideration about a hanging pendent, but i dont have anything to hang it on to with out the risk of it falling or coming lose from its attachment on the wall.

 

[marinefish]

hey broomer,
my question is, if the 250 watt metal halide is mounted about 9-10 inches off the water surface and having two clip on table top fans circulating the air in the cannopy, would i still have a heat problem?
also, other then buying a chiller, what other method can i use to chill the tank in the event that i have a heat problem?

 

[broomer5]

I don't think that having two clip on fans - that are just moving the air around inside the enclosure - would do much to get rid of the heat.
If on the other hand - you installed fans in the top of a canopy, blowing OUT - and allowed cooler room temperature air to be drawn in low - and pulled across the lamp ..... then you might be able to evacuate much of the hot air.
Otherwise .... I still think having one 250 watt halide in such a small box is going to raise the temperature of the water.
There's no way to eliminate the radiant heat at the water surface ( without reducing the intensity of the light ).
It's the hot air that will transfer heat to the water surface that I'm normally concerned about.
It's true that evaporation will cool the water - but you gotta heat it to evaporate it.
I've never had a set up like this .. so please understand this is just a guess.
Hopefully someone here with a set up like you plan will share their experience

 

[sebae0]

hey marine i had 2 250w mh hanging over a 50 gal with an open canopy and i had heat problems. what i did wrong was only put one fan on the top drawing air out, guess it didn't move enough air out though. what i did to fix it was to put 2 fans on the canopy but on the sides, one blowing in across the bulbs and the other pulling air out. remember though that this is a open canopy and yours is closed, but it did work alot better that way.

 

[marinefish]

the miniture clip on fan is gona be blowing air room air into the light directly, i was wondering will this work enough?

 

[marinefish]

hey sabae, when you say open cannopy what do you mean? mine is open the whole entire back end of the cannopy. what kind of fans do u you use on ur reef tank? what size is your fan? how high up are your lights? and at what temp is ur tank held at constant?

 

[sebae0]

by open i mean mine hangs down from the ceiling in my basement so it is open all the way around the top now. my temp stays a constant 78 now but with warmer weather coming i expect it to increase by about 2 degrees. i think if your canopy is open in the back and you use 2 fans you"ll be alright. the fans i'm using are pretty big prob. 5" ones, i got them out of a 02 concentrator at work. my canopy is now over a 180 gal tank so its 6' long also. hth

 

[bang guy]

IMO the best way to cool a tank is to point a fan across the WATER. It's the water you want to cool, not the bulb, not the canopy.

 

[sebae0]

marine here's a pic of my canopy.

 

[sebae0]

forgot the pic!

 

[marinefish]

thanks for the pic sabaeO. that really helps =). my final question is, if i go with the 175 watt, how high would you recommend that be mounted away from the water surface and if i go with the 250, how high would you recommend that be mounted from teh water surface?
sorry if i sound repeative, but i really want to get this right cuz its a lot of money to buy a metal halide. thank you for your patience =)

 

[sebae0]

my pleasure marine, i think mine are like 7.5" away from the top of the tank. i wouldn't worry to much as long as your atleast that far away, i have splashed a little water on the bulbs unknowingly and nothing has happened to them. you know messing around in tank and oops there goes a litle water on the bulbs. like i said b4 go with the 250w they offer you more options and for 16 bucks why worry. good luck and keep me posted.

 

[sterling]

If you have a ballast that will handle up to a 250W, for your size tank I'd put in the 175W and if you get a larger tank sometime you then can upgrade your bulb.
Your water is going to heat up more with 250W over it.
JMO

 

[marinefish]

thank you all who have help me in this matter. i really appreciate it. i have come to a conclusion that 250 watt is a good choice to go with. thank you all for having the patience with me and who have put up with my repeativeness. you guys have help me a lot repeatedly. i will keep you guys posted as i progress. =)

 

[bang guy]

Good luck to you. You should have some happy clams. If you have heat issues remember that fluctuating temps are much worse than high temps.