Flies, matter very little, grilse will take most of the usual suspects. Stoats Tail, Munroe,Shrimp patterns, Willie Gunn trad and tied shrimp style. If the water is low keep the flies small, 10s 12s I would go as far to argue if you are getting no action it is not the flkies that are wrong it is just the grilse have gone.
Down and across on a full floater, may be a polyleader if I was just above the tidal reaches.
Finally try a Collie Dog/ Sunray shadow worked fast across the pool, if you don't get a follow there are no grilse there.
I think of grilse as gangs of teenagers, full of energy and life with an IQ about the same as their age. Cannot sit still and chase and torment anything in sight.