I never had geckos but when i had my other lizards i had a 80%reptibark and 20% calcisand subatrate (just split the floor space). the sand was under teh heatbulb and held the heat well, one of the lizards would partially bury itself under the light when basking. Both lizards seemed to use hte sand as their toilet area which was also good as it is really easy to spot clean
We would release their insects into the reptibark end of their vivs, occassionally the insexts would reach the sand before getting eaten but generally they were eaten on the bark.
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