Oh, Sorry, it should be Tetra rather than Detra, my spell was wrong. I live in Amsterdam, the German brand Tetra seems to be the only commercial frog food in the pet store nearby. It costed me 5.9 euro! (just 36g), much more expensive than commercial fish food with the same weight and brand. Also in my homeland China, Tetra is a popular aquarium brand.
I will be careful when I get food back and just feed them tiny food. Thank you!