If you look at these shrimp closely, you will see they have large fans on their front pairs of legs. This is why they are also called Fan shrimp. The fans have many tiny bristles, which serve to catch minute particles of food from the water column. They sit in one place, usually where the current is strongest, and wave the fans in the water, then close them & wipe them across their mouth to eat what they caught.
You can feed them micro or banana worms, copepods, rotifers, cultured liquid algae, Golden Pearls in the 5-50 micron size, even bakers yeast dissolved in water first, but you have to be careful with it, can't put too much in at one time.
Best to turn the filter off to allow them time to harvest the food. Say for an hour or so, maybe 3x a week. This means having an accessory pump that runs all the time separately from the filter, to provide constant current for the food.
You can also feed liquid Phyto, sold for feeding marine corals, or pure powdered spirulina, mixed in water first, or spray dried algae or spray dried crustaceans. Those last two are made by Two Little Fishies and they cost a darn fortune, both are for marine tanks but work great for any filter feeding animal, such as the fan shrimps or FW clams.