Yeah, that was my guess, but you can also just dump the Phytoplankton in the water. I would be surprised if he is not using any kind of invertebrate food at all in the tank. His profile said his tank was 3 meters which seems off because that is like 10 feet.
Mine is 125 gallon, but I don't think they need much space because they don't move much. Just need to have good water quality and phytoplankton to feed.
After 2 years his looked a little small to me. They need calcium to grow their shells.
I would advise against getting one because there are so few success stories.