The temp gradient is easy based on depth of substrate, but there is more to it then that. You have to look at type of substrate depending on the species,mulitble locations to choose from, moisture levels, etc... I am by far no expert so keep that in mind, but even the experts will tell you they cant offer ideal nesting to suit the monitor completly as well. So far I have breed Glauerti,Rudi's,Ackies,Argus,and Gouldi/Flavi crosses. All have given me eggs but the only one to even come close to a decent nest was the Gouldi cross. So I have to be happy with just getting fertile eggs in any kind of nest,good or bad.
Good Luck,
Robert
