Krish, looks like you've got some thermodynamic blues. Let me help you understand how a fan cools the water. I'm gona try to do this in standard units because it seems much of us use them, and it will make it about 10 times harder for me, and I enjoy that.
Ok, multiply the volume of your tank and sump in gallons by 9 ((4.18kJ/kg)/((2.2lbs/kg)(8lbs/gal)5/9F/C + compensation for rock)an approximation trying to compensate for the differnent specific heat value of the rock mass in your tank) This will give you the amount of kJ needed to change the temp of your system by 1degF, assumeing your house is roughly the same temp as the tank.
So, how do fans remove energy? (kJ?) By evaporation requireing energy to happen, and the place it gets this energy is from the heat of the water. The air directly over the surface of the water is always saturated with 100% humidity, but its rapidly defuseing into air layers above it. The purpose of the fans is to provide a steady stream of new air which isnt saturated at 100% humitidy to the boundry layer on the surface of the water. So, when you are considering fan placement, keep in mind all the circulation in the world of air saturated at 100% humidity doesnt really do any good, so place fans accordingly.
Evergy ml of water evaporated pulls out about 540kJ/g (some of you may wonder why I say 'about', but after some thermodynamics you will understand a PdV work required to expand the water into its gaseous form changes things slightly, so its actually just 'about 540kJ/g). So, to change this into terms easy to relate to aquariums, everytime your fans evaporate 1 gal of water, they are 1188kJ of energy removed from the water.
Now, there are some other huge factors like ambient temp around the tank, along with the rate of airflow in the room, combined with thickness of the acrilic and flow patterns in the tank etc etc. But that stuff its really challenging to calculate, and if ambient temp is below the temp you wish to acheive, its not going to be the cause of the problem.
So, if you ballence the large amount of heat the tank is getting with an evaporation rate that I showed how to calculate above, then you can find a thermal equlibrium point that meets your needs.
A few things I noticed above, first I want to say that when you feel a submerged or partially submerged, and it feels cool to the touch, guess where the heat went? Into the water, all those pumps are effectively water cooled, and that means all the extra energy goes into heating the water. I dont know what pumps you are running, but it could easily be like haveing a 50watt+ heater running continously in your tank.
Now, the halides, WOW, halides are just like above tank mounted heaters. You may find the most cost effective and energy efficient solution is to swap the halide setup out for some T5s. I know when I had my halides, temp was always something i had to worry about, after swapping to T5s, that whole issue just dissapeared, and I was able to stop dicking with fans and things. The combo effect of buying a chiller$$, which is a large power drain, and dumping tons of wasted energy in heat into the tank with the halides would be getting a little silly (IMO at least).
Best of luck to you my friend, and if you have any questions I can help you with, its never a burden.
