And yet Tubby is very tubby! haha I'm not sure yet, since there's no sign of Skinny being mature. He/she/it was so very tiny when I got him/her/it that I think Skinny is just a few months behind Tubby in age.
Skinny and Tubby vanished on me the first couple weeks I had them. Scared the life out of me several times, and I ended up tearing apart my tank just like you. I eventually got used to it and learned that they would come out when they learned the feeding schedule. Now I can always find them, no matter where they hide!
I just saw something curious that I wonder if anyone has seen. I just finished doing dishes and walked back into my bedroom to see Tubby up at the surface, sticking his nose and mouth above the water. He was just kind of hanging out there. Not only is my ceiling light on, but the lights in the tank are on as well, so its very bright in there. Given that ADFs are a nocturnal species, I found this very odd. Coupled with the fact that Tubby took a tumble just the other day, I want to make sure this is nothing to be concerned with. As soon as I started to take off the lid to make sure he was ok, he freaked and dove back under a resin log, so his reaction time and speed are up to par.