Glass tops and bright lights can provide a food source

I use glass tops on all my tanks as it gives a nice clean look and glass tops can with the aid of a plastic strip be customized to give your tank a very tight fitting lid to keep critters from climbing out of the tank. Combine this with a good light level (I use a twin bulb T5 fixture with one 10000k tube and one actinic tube) and a couple airstones with enough air running through them to mist the glass top and you get a breeding ground for green algae (I get a gelatanous form) which you can scrape back into the tank and the shrimp will eat it up like giving people food to a puppy.

This algae floats, but is a little sticky so I usually scrape it into the tank and then stick it to a plant or decoration.

Dave