Oh don't worry about the rock thing! If it eats wafers, that's fantastic. You could still grow the extra algae for it if you want to, but it's the oto's that don't eat supplements that you really need to do that for. I would start supplmenting from time to time with veggies like blanched shelled peas and zucchini. If it eats wafers I would expect it should take right to veggies as well. You can use just regular frozen peas and microwave them in water until soft, then pop the shells off. I mic my zucchini in water until soft as well, just cut it into strips or discs so they can get at the inside.
So the shrimp will be going into the 2.5 gal
..is that a glass tank or something like a minibow? If it's a minibow, you can screw a regular household CFL bulb into the socket instead of the standard aquarium incandescent bulb. Look for one that is about 10 watt and specifies that it is 6500k or better. Your shrimp will do fine with any light, or even no light, but if you want to grow plants in their tank this bulb will allow you to do that.
How many cherries are there? It's possible there isn't a male/female pair. Do you know the pH and temperature of their tank?