This weekend im going to be setting up my 300 gallon 6'x4'x1.5' pond and im going to be relying on plants for filtration. im going to be getting comets and mabye a fantail or two. im going to put river rock in the bottom and a clay pot here and there for hiding places. im going to want a scavanger in their also so should i get a bullhead or crayfish or both?