Wouldn't removing the lids increase the risk of fish loss due to jumping? I have hatchets and zebra danios so that is not an option. In Oregon most houses do not have central air, especially rental units. Finally, you have to consider that window AC's only work if you have windows that open up and down, rather than side-to-side. They do make portable air conditioners (don't go in the window), but they still have to vent outside and they cost $400-$800.
I am dreading the summer but luckily it only gets to a 100*F or so for a few days, usually it is around 80*F. Increased aeration is my plan. And maybe a fan blowing on the tank, but with lid still on?
I have read that you should turn up your heater to match the usual daytime summer temperature so that your fish aren't stressed by a sudden heat drop at night. Idea is that the fluctuations are more harmful than sustained higher temperatures, which makes sense given the standard heat ICH cure people use quite regularly. Of course, that is usually only for a couple weeks at a time, so I am not sure about long-term effects. Anyone care to comment on this?