I've got a 9 year old paddletail who's been refusing to eat and exhibiting some really worrying behaviors. She seems very lethargic, yawning and snapping as if she's about to shed but no evidence of doing and swishing her tail. I tested the levels in her water and the nitrates were very high so I've cleaned out the tank and done a partial water change. I can't see any physical changes on her skin or eyes. She last ate 4 days ago. Any help or advice would be greatly appreciated, I'm really worried about her