Hello, Dorothee,
they eat algae and detritus, e.g., dead leaves of water plants, oak and beech leaves on the ground, and – what’s very important I think – they eat dead mosquito larvae or other leftover of live food which is no longer alive … 😉
I feed them only tiny bits of food tabs from time to time – more to get an opportunity to “count” them than to feed them – to lure them out of their hides and to see how many young and old shrimps are in the tank.
I got mine from here – I think it’s the same shop you mentioned. I’m afraid I advertised them too much ……. the simoni-shrimps are out of stock at the moment …..