It was on another forum :p
Copy, paste;
The problem is that those mini fridges just don't move enough heat. You'll be lucky to get 100 BTU/hr out of it. Remember, they are designed to cool a fixed volume and expect the door to be closed most of the time. In essence, by pumping water through it, you are leaving the door open.
If we assume all of your tank components add 300 watts of heat to your tank, that's 1,023 BTU/hr you need to pull out. That's 10x what a mini fridge can do. Even if your equipment adds just 50 watts of heat, that's 170 BTU/hr almost double what the fridge can handle.
Unfortunately, that approach simply isn't feasible for a tank much bigger than around 25 gallons. If you compare the amount of heat the mini fridge can pull out (100 BTU/hr) to a very small room air conditioner (5,000 BTU/hr) you'd be better served adding a small air conditioner for that room and keeping it cooler.