If you still need help here's what I do...

To keep food from falling between the rocks I use a teabag dish. You can use any form of ceramic plate, terracotta saucer etc.

I fill a small cup with a little tank water, drop a pinch of pellets (and also mix some some bloodworm in once or twice a week) in and use a turkey baster to suck it up and direct it down onto the dish. They learn very fast to go there for food.

I give my frogs about 3-5 minutes to find the food and eat it. If there's any left I take it out, if it's gone very quick I put a teeny bit more in for them