There should never be enough food in the tank where it sits for more than a few hours. I have some white pearl shrimps, and one way that I can tell whether they are getting enough food or not is just by looking at them. They are see-through, and I can see whether their digestive tract is filled with food or not. If I look around the aquarium and see many with empty digestive tracts, I put some more food in the tank. Sometimes I will go days without feeding them because I see that they are finding enough food on their own.