I am starting my first grow with coolers. We have been having very unseasonably warm weather. I find that ice bottles help me keep the res at 65 when the room is at 72 or 73, which is really all I expected it to do. But if I let the room temp approach 80, the ice has a hard time keeping the res at 75.
At least in my environment, I have to use whatever AC it takes to keep the room temp low 70s so ice can keep the res below 70.
Another thing, the lights are adding heat to your res so it's the insulation on top that matters most. And, if you don't have an air cooled hood, that alone can be worth 4 or 5 degrees in the res.
That's my experience so far, and here's a question - My ice bottles float around and I want to keep them away from roots (which are just now getting into the water). Do most of you weight them down? or have any ideas for making an ice bottle holder that keeps it vertical in one corner?