A friend of mine gave me a very large but very nice piece of red sandstone type rock for my Bearded Dragon.
To make a long story short, the thing is large and heavy enough that I had to keep a CHE radiating onto it all day and all night for it to do what I wanted. If I shut all the heat sources off it would take too long the next day for the rock to heat up again.
Now that I leave the CHE on 24/7 the rock does an excellent job of distributing heat around the cage. I have lights that bring the total temp up to suitable basking levels.
But, my cage has a solid top with a false-ceiling. Even though it's about the same ventilation as your cage I'm able to reflect some of that heat back into the cage.
You may have to modify that screen top. If you're not using tube-type bulbs you could cover most of it with aluminum foil. You could still do that with the tube bulbs but it won't work as well.
>>I've purchased a 75 gallon tank for my bearded dragon...it is 48"x18"x24"...the substrate is ceramic tile...the temp of my home is 75 degrees...I have a screen top...
>>still working on getting the right light for the right temp...
>>trying spot lights and flood lights...starting to feel like he'll never move in...
>>any suggestions on a good type of rock to get for basking spot...had two...took days cleaning and drying to be on safe side,only to find neither retains heat well...
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Current snakes:
0.2 Gonyosoma oxycephala - (Silver/Yellow)
3.3 Gonyosoma oxycephala - (Green)
2.1 Gonyosoma janseni - (Black)
3.3 Gonyosoma janseni - (Black & Tan)