Well kelvinng01 from you have said so far, I say the reason your fish is not eating properly is because your water parameters are out of balance. 80% per week is a lot a pouring anti chlorine in the tank then filling the tank straight from the tap is not the best way to do things, and most likely contributing to stressing the fish.
Have a good read on how to cycle and maintain an arowana tank. There is lots of good info from many members who have contributed their experiences. Out of all the aquarium forums dedicated to fish keeping of larger fish, this has to be one of the best.