Ok I got breathers for three of my group. I noticed when I use them that they leak. Is the Collasium a timed dungeon? Is there some place to recharge breathers?

there are quite a few air pockets located through out.

The Collasium does have a time element in that your divers can only hold their breath for so long before drowning and taking damage. If you equip both the underwater helm and the conch shell, then you can hold your breath even longer.. There are also plenty of airpockets littered around the dungeon, although these might prove elusive at first!

Also - bear in mind that you can use the breath of air (vine level 6 spell) to replenish air levels, and the cure spells to heal back that caster..