I had two turtles (male and female) and five goldfish in one 2.5 x 1.5 ft (around 46 x 61 cm) aquarium, which was filled with water up to 1 ft (around 30 cm) height. I fed all of them once a day, everyday in morning with protein Toya food (fishes also like it). But one evening one of my turtles ate one of the goldfish and left its corpse behind (few months ago even corpse wasn't found in water, when fish was small).
Why are they attacking the fish when I am feeding them daily? How can I stop it? I don't have a place to fit another aquarium for either the turtle or for the fish. Should I bring another bigger species like a frog or bigger fish that can guard the goldfish? The turtle who ate the fish also attacks the other turtle's feet and neck.