Hello. This is my first post so I hope that I am posting in the correct spot. I have had my tank for about a year now and never had anything bad happen except a slight case of ich that went away quickly. In the last 48 hours, I have lost a total of 2 Damsels, a spotted dottyback, 2 clownfish, an Angelfish, a peppermint shrimp, 2 snails, and my last 3 which are Goby’s are all on their way out as well. They are all suddenly covered in Ich, and my Firefish goby has an ulcer looking thing on his tail (picture attached). Anyone able to help identify so I can try to treat?? Or is it beyond treatment?