Freezing water in a water bottle works for me. On hot days I will place one in the tank during the afternoon. It lasts a good 3 hours. Which is usually enough for the very hot hours. I am sure the larger the container the longer it will last after the water is frozen inside. And its reusable!
I also change my lighting hours. I will block out the sunlight during the morning (to increase dark hours so the fish don't get stressed out by the constant light) and turn the lights on when it has cooled off during the evening.
As for too hot. I have had my fish survive 90 degree temps (only for 8 hours though). Fish are usually very hardy against temp changes, its most likely the corals will go first. I also have had a constant 83 for a week in a row one time with no horrible effects.
Luckily, its way easier to deal with too hot rather than a broken heater when its too cold. As I found out the hard way.
I also change my lighting hours. I will block out the sunlight during the morning (to increase dark hours so the fish don't get stressed out by the constant light) and turn the lights on when it has cooled off during the evening.
As for too hot. I have had my fish survive 90 degree temps (only for 8 hours though). Fish are usually very hardy against temp changes, its most likely the corals will go first. I also have had a constant 83 for a week in a row one time with no horrible effects.
Luckily, its way easier to deal with too hot rather than a broken heater when its too cold. As I found out the hard way.