Amy,

I use the 100w on my 24h. I ended up switching to it because the 60w could maintain the temp fine, but had a hard time recovering from the temp drop I did over night. the 100w can easily heat my 24x18x24 tank and recover quickly from a temp drop over night

Just make sure the dome you have has a ceramic base or the CHE will melt it. If money isn't really an issue than I would recommend the HydroTerm over the thermostat I linked in the other thread. It has the ability to program a daytime and night time temp. It uses a photo eye to determine if the lights are on or off in the room and switches temp settings accordingly.