Have a pygmy Yellowtail Angelfish that has been in my 90g. tank for 6 mos. He is suddenly being aggressive toward Chromis and a few of the other smaller fish. I have not added any new livestock in over 3 mos. except for a couple inverts. Why the behavior change? Have tried yelling at him, but no luck. I'd hate to get rid of him as it's a great looking and healthy fish, but he's being an a....hole.

