Your hex cover wasnt vented at all? Not even for filter systems? I have a hex tank aquarium lid (same deal as you, 35 gal hex) The tank lid had a removable part in the back to fit the filter system in though. I covered that part with screen and that is my tank vent. I also have a laptop cooler fan that I put on the top if the humidity gets up a bit too much (first week that I had the tank set up with no frogs in it, humidity was hitting 90%)

When you find your frog, which I REALLY hope you do, I'd put them back in their old enclosure until you can get a cover situation figured out.

Good luck!!