I have two seng. in a 75 and they look like they are scratched.. One has a line and the other has a small circular area...I only have two river rocks in there, and one of the "texas hole" rocks. I dont think the bristlenose is messing with them, would a four- line be able to bite them?
I really don't know what their skin looks like if its been damaged is the main problem...
I really don't know what their skin looks like if its been damaged is the main problem...