The aqua cavern from Caverns 2 mod has bedrock below and above it like the nether, a player found the bottom of the 2 ladder dungeon and followed it from Y 10 to Y 256 above bedrock.

Hmm, that should not happen ^^, I wonder why this has not happend in the nether yet...

could be yes, as I am searching for air to end the tubes.

If bedrock..then end currentpos-10?

yep the current solution looks pretty much like that xD

Is it because this dim is full of water?

This should fix it: 26.3.137