Can't keep temp constant

[Rig]

Hi, I'm having a lot of problems keeping my temperature constant and can't really figure out why.

Tank is a 26G with 2 MJ1200s and a Rio 200 in the tank generating some heat. Theres a 150W MH about 5" above the glass that completely covers the tank. I have a big fan blowing directly across the tank that generally takes care of the MH.

During the day my tank stays about 79.9 pretty consistently. At night, it jumps to 83ish, and for the life of me I cannot figure out why.

In my cpr hang aquafuge I have a Iceprobe chiller drilled into the area where the water flows in, and a 100W heater in the compartment where the water leaves. So the incoming, hot water, gets chilled, then heated, maybe, and then ejected into the main tank hopefully at a coooler temp. I've tried setting the temp on the heater a little lower, like 78 degrees, so its not negating the purpose of the chiller, but this doesnt seem to work either.

I have the fan turn off at the same time as the MH bc its loud and annoying to sleep 8 ft away from, but with the only dif being the mh and the fan going off, I dont see how the temp could go up 3-4 degrees? Especially when the temp is going higher than the heater is set for and my apartment is not getting above 75 degrees.

Could this mean theres a problem with either of the maxijets or the rio in the tank? Thanks for any advice, hopefully this makes sense to someone.

[Samper]

You say you have a glass cover over the entire tank? If so I'd make sure you don't have any fish known to be jumpers and remove that thing for starters. Your light will penetrate better, gas exchange will be better and it may fix your temp problem. I know the fans are loud and I had the same problem for a while....turn it on one night and just see if this helps the problem...after a while sleeping with it on you won't be able to sleep if it's off. Just a thought.

[Meric]

You may want to double check your heater. I had (2) Heaters that when you set them to 78 degrees, they were miscalabrated and would heat the tank to 84 degrees. I had to set the heaters to 73 degrees just to keep them from overheating the tank.

[Rig]

I'll try running the fan full time see if that works. I'm also gona swap out the 100W heater in there for a 50W heater I have laying around. Maybe that will help. Option 3 is getting one of those reefkeepers. They seem like a really solid product.

I have a 200$ golden dwarf moray in there, so this tank is needing to be sealed 100%. I'd be pretty pissed if he made it out. Thakns for the replies.