I think if you run the chiller a bit longer as Bill states it would be ok. I would assume the main heat source is your halide and that as you aren't running the halide 24 hours a day the chiller will probably only have to cycle a few times during that lighting period anyways. You can always just try it and if the chiller is only turning on for a very short period of time take it off and save it for your bigger tank.

If you go with fans instead of the chiller, just be prepared with a lot of fresh top off water as you will have a lot of evaporation. I added a fan to my sump now that it's getting warmer and instead of adding water every 5 days I'm having to do it every 2 days and that's on my little 45g. Do you have a fan blowing on the metal halide light or in your hood? I have a small fan that is on a timer based on my metal halide light time cycle that blows straight at it. The fan starts when the light comes on and then runs for about an hour or so after it turns off. This helps circulate some of that heat out of the hood and away from the surface of the water.