I have a 29 gallon tank with 2 angel fish in it. One is white and athe other is a marble. The white angel torments the marbel angel keeping it in a corner. If it ventures out the white angel rushes over to it and shoves it back into the corner. I have to stand at the aquarium to be sure that the marble fish gets enough to eat. Is this normal and is there anything I can do to stop the behavior?