I purchased my silver arowana a week ago and he/she was swimming around with 4 neon tetras and a plecosomous. He was always swimming on the surface of my 30 gallon fish tank and seemed to always open and close his mouth constantly. He has not eaten anything since I have bought him/her, and now he stays at the bottom of the tank, barely swimming around. He does not open and close his mouth anymore. I tried feeding him/her pellets, crickets, and blood worms. He/she has not eaten any of those items. Does anyone have any suggestions? The chemicals (nitrate,alkalinity, ph and even the water softness is fine). I have also noticed that he/she sometimes swims backwards. Can someone please give me advice to help my silver arowana? Thanks