Snail Food(Nerite Snail)

[BaylorPerez]

So i was looking on the web and i came across a listing for snail food. It said that snails(specifically nerites) eat phytoplankton, especially algae, Cyanobacteria, Diatoms, Film Algae and vegetable bits. while using Supplement food of Nerite Snail with the small bits or the flakes of cucumber, blanched spinach and lettuce, and corgette.
 
Is this specifically true or is their other "food" that they eat that is safe and non-harmful