I'm struggling with the heat here in Japan too
Due to work, I can't use the ice bottle idea.
So I bought a couple of fans to increase the evaporation rate and thus cool down the tank.
Initially, I was a bit skeptical if it would work,
I rigged them up around 12 hours ago and the temperature has dropped from 30° Celsius to 26°
But as have been mentioned, you need to top up the water quite frequently.
Due to work, I can't use the ice bottle idea.
So I bought a couple of fans to increase the evaporation rate and thus cool down the tank.
Initially, I was a bit skeptical if it would work,
I rigged them up around 12 hours ago and the temperature has dropped from 30° Celsius to 26°
But as have been mentioned, you need to top up the water quite frequently.