I recently bought a platy and a crab for a semi-new (2 weeks old) 5G aquarium that I have set up. The problem is, whenever I put food into the aquarium, the food circulates on top and then gets pushed to the sea floor of the aquarium by the filter. They crab then scavenges around for about 2 hours collecting all of this food, while the platy gets none. Is there a reason that my platy won't eat food from the surface of the water?? thank you in advance