Depends,
If the tangs are established in the tank, healthy, no pinched bellies, hlle etc etc, a few times a week/every other day is okay if they have adequate rockwork/room to graze.
If its a new addition, or is a baby /juvie, Id recommend everyday, and even twice a day in cases example- the half dollar size hippos you commonly see for sale should ideally always have nori offered to them.
I wouldn't recommend soaking foods like nori in garlic regularly long term, as it can possibly lead to renal function impairment in some fish.
If it is used as a enticement agent for a picky eater short term is no problem and useful.
Long term, Selcon is my go to nori "soak" but ideally food soaks/vitamins would be used with pellet foods.
Just my .02