You don't have to do any thing at the Alter of Seran, it will heal you if you need it and if your on a quest to find it then the quest will be given for just finding it. If you are on Paladin training then just talk to the alter and go back to town to get you Paladin.
As far as more re-breathers goes, just keep taking him more conch shells for, every three you take him he will make any combination of masks or re-breathers.
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......shake it baby.