Either.
Personally, I don't usually feed my snails because that encourages them to keep up with the biofilm and algae growth. From what I've been reading about the shrimps, a lot of people use the Nori strips for their shrimps because it also contains calcium as well as a lot of micronutrients which the shrimps need for their shell creation and overall health.
Spirulina is the main algae in many algae based dried foods ( flakes, pellets, blocks, etc). You might want to try some spirulina flakes along with the Nori strips. ( I also read that the shrimps don't all rush over to the Nori but over time, they find it and you will see them on and eating the strips. )