Is it true that canister filters cause hole in the head for cichlids and bio-wheel filters don't? I am using a canister filter for my oscar (without carbon) and the hole in the head doesn't seem to be healing. Could this be from the canister filter? I am using metro and feeding hikari cichlid gold and doing regular water changes with water conditioner and using aquarium salt with the water temp at 83 degrees for faster healing.