I just got 3 flower shrimp (bamboo) in my 20 gallon. I've got a current (bought an Azoo powerhead that someone recommended on this site and its been great) and it is heavily planted. What if anything, do I need to feed these guys? My fish get a variety and my cory cats get algae wafers. Do they just filter feed or do I need some really small stuff to put in and float around in the current?