I have a 70 gallon aquarium, fully cycled. I had this regal angelfish 2 weeks ago, first she never ate, step by step I've let it it, & till two days ago she was eating like a pig, she ate everything. Since yesterday, she's extremely lazy, she's not active nor swimming as it used & she never ate since then. She's a juvenile 4", physically she's 100% normal. Is she dying!!!?? Or how can I help?!!! Other livestock in the tank include a school of blue green chromis & a 3" sailfin tang. To be mentioned few aggression from the sailfin tang, but not so much & it's from day one, & as I see it started to improve. Any help?!!!!