That's all you can do then.
Don't use ice cubes or bottled ice water its a complete waste of time. It just stresses the fish will altering the temp all the time.
i have two cory's in my tank, which is at standard temp of 26.c, depending on how long
the light has been on, can get between 22.c - 28.c and they are fine, just reduce sunlight and
tank light, thats the best thing you can do as Wilder said