5 gal tank w/ ADF, shrimp, and maybe a snail?

Welcome to the Fish hobby! You could always try ghost shrimp, they go for about 5 per dollar at superpets and like 4 for a dollar at petco. How big is the tank with the angelfish? The frog could have died from stress, angelfish are fairly aggressive fish and will compete for food. What king of food are you feeding the frogs? It really depends on what kind of carpeting plant, frogs will most likely spend most of their time either at the surface or resting at the bottom, so chances are they'll find their food. Good luck:)