Underwater weapons
My Trident is Rabid (earth) and my Spear is Berserker (force, but going to change to fire to increase AoE utility). I don’t carry alternate weapons for builds as I see the weapons damage type niched.
As for aqua breathers, best is yellow from Tequatl (unless TA added some), but green karma is the main bet. Key is getting the lvl 80 one so you can equip the proper runes/orbs.