Or a bit of algae wafer if you said you only have two. If your tank has been up for several months 3-4 or more, then you may not need to supplement much, but I would do it a area the fish don't normally hang out in, or it night when the light is off. Shrimp graze all day. On rocks and plants. See if you can find Hikari Crab Cuisine, our Petco recently started carrying it. Break it in 2 pieces for them and see how fast they eat it.
My shrimp will grab the piece and try and run off with it.
You can usually get Hikari Shrimp Cuisine at good lfs, or just order online. It is expensive but good, and it will last almost forever with 2 shrimp, lol If you have a male and female maybe you will get more shrimp. These size of these pieces are very small and shrimp sized.
The Crab Cuisine are shaped more like a stick.
I would also add a chunk of cuddlebone from the bird section (plain not treated or flavored), size of a dime or quarter (you can use a big knife to cut apart chunks), it will float and sink after a few days (can then place it in the back to hide it or leave it in the front to see how much they nibble it). Good for snails and shrimp.