I'm glad that you have figured out the issue.

Leaving tap water out no longer removes all chemicals and heavy metals from tap water. While chlorine will evaporate out in 48 hours, Chlorimines, ammonia, and heavy metals will be left behind therefore you must treat the tap water.

When using a UTH for burrowing frogs place it on the side of the tank just above the top level of the substrate. A 40 watt infrared bulb is just fine to combine with the UTH for supplemental heat. 40 watts is just fine you don't want to go higher than 50 and use a lamp that has a dimmer switch like the Fluker's 5.5" clamp lamp with dimmer.

I hope all this helps and if you have any further questions just ask.