Small suggestion
I’ve been running this dungeon for a while now during the hunt for a shiny clamperl, and I’ve noticed it makes little sense that Shellder and Seel are only recruitable from Floor 1-3. Floor 3-12 has no recruits whatsoever before Floor 12 starts having recruits again.
Shellder and Seel being only recruitable on the first 3 floors is a little odd imo, unless there is a specific reason for it. This is why I propose to make them recruitable at floors 1 through 12.
This is strange. I have noticed this on a much lower dungeon. I just ran Happiness Lake and for 4 floors in a row, it said there was nothing recruit-able. Could it be perhaps because of your level? Are you already level 100? In that case, then, are you using a bunch of AoE moves to clear rooms. It could be just glitching out. Take your time next time, and see what you can try differently to get the game to act how you see fit. 
I’m not exactly sure what this reply means, but I’ve confirmed that there are no recruitable pokemon between floor 3 and 12 in Iceberg Frigid Waters - I’m using level 100s in my team. The wiki also confirms the same thing. I know how the recruit system works!
I’m sorry. It was not my intention to perplex you or cause you any doubt. I was seriously asking you to keep testing the game in any dungeons you may run. See if any similarities or patterns pop-up. I’ll do the same and roll a spreadsheet of dungeons to level layout so everyone will know exactly what floors to avoid when farming.