Ive had a saltwater tank for 8 yrs, upgraded to a 55 gal 4 yrs ago. Now i am upgrading to a 120. My tank is set up with some of the rock from the 55 gal. After 10 days I added 3 dominos, striped goby, blue damsel, firefish from another smaller tank and a 5 yr old clown. The dominos went after the smaller domino nipping its tail. They no longer pick but now the tip of the tail is white. I am wondering if it is tail fin rot or a fungas. I have not experienced this before with my fish in the past. Is this contagious?