I actually felt sorry for you cause smu666ler is getting all kinds of posts for his pretender but you're getting no love.
I'm by no means an expert but heres my take based on what little I've played of them and what some other players have suggested.
I hate that their sacreds are ocean only. That said, try to dominate the oceans with lots of triton knights. Can't say what bless works well with them (besides W bless) I would add astral bless for the MR myself. They already recuperate.
When you're ready to tackle land provinces I just pump out mermen like they are going out of style. Try to research conjuration for some summons. (Sea King comes to me at the moment.) And recruit indies to help where you are weak. Which to me is everywhere BECAUSE YOUR SACRED TROOPS ARE WATER ONLY!! Did I mention I hate that?

Though I suppose fish amulets are good at bringing your amber mages and bishop fish and triton princes to help out on land.
That's really the best I can give you. I'm sure someone with much more knowledge can be better help.