I got Metal halides, and now my tank is too cool!

[kbohip]

I finally, after having my tank setup for over a year got a dual 250w metal halide system for my tank. At first the heat was an issue so I installed a 120mm dc fan in the canopy. The fan drops the temp so much that the 250 heater has to kick on just to hold 75F.:rolleyes: I've been turning the fan off and on to try and keep the water temps between 75-78, but I'm not sure if these temp fluctuations are messing up the tank inhabitants. The fan has the capability of cooling the tank by about 1 degree an hour. This is also about how fast it heats back up with the fan off.

Should I just leave the fan run all the time and try something different if it gets below say 74F? The only other thing I can think to do is buy an even lower cfm fan in the hopes that it stabilizes the water temp. I know that temperature fluctuations are very bad for the fish, but I'm running out of options here on how to control it.

[lastin1]

What are you using to power the fan? Have you thought about getting a variable power supply to vary the speed?

[HornetMech242]

Or get acontroller that you can plug the fan into and will turn the fan and the heaters on and off based on water temp.

[kbohip]

It's a 12v fan and I'm using a 9 volt transformer off of an old cordless phone to power it. The fan is a Panasonic Panaflo from my pc buiding parts bin. It's a medium speed model so I can only surmise that at 3 volts less than what it's supposed to have, the fan is already spinning slower than normal.

I like the idea of a variable psu though, don't know why I didn't think of that. I may go down to Radio Shack and pick one up pretty soon. Failing that, I'll look into what you suggested HornetMech.

[herostar]

You could get a cheap digital timer ($10 at harborfreight.com) and set it to go an hour on/hour off while the lights are on... The timers work well. I use two of them.

[sditch]

What a nice problem to have, first I would check your temp probe and make sure the readings are correct(May want to place the probe in the return area of the sump). Its hard to believe you can drop the temp 1 degree an hour with canapy fans.

I use a AquaController to control fans but you should be able to just turn on the fans on when the halides come one and be good.

If you temp drops one degree with the halides on you a lucky man :)

[kbohip]

<a href=showthread.php?s=&postid=12667347#post12667347 target=_blank>Originally posted</a> by herostar
You could get a cheap digital timer ($10 at harborfreight.com) and set it to go an hour on/hour off while the lights are on... The timers work well. I use two of them.

Ha! That's hilarious! I was JUST at Harbor Freight yesterday and picked up two of those exact timers! They had them on sale for $7.99. The only problem is I got home and found one to be defective. I guess they're battery powered and non replaceable batteries.

Anyway, another great idea herostar. I'm going to do just that and see what happens...after I get another HF timer.;)

sditch, I'll put my temp probe in the sump tonight to make sure these readings are accurate.

[manderx]

get a controller for sure. such a waste of energy to have your fans and heater fighting each other. and that's only 1% of the coolness a good controller will give you....