in nature arowanas will eat almost anything from bugs, to fish, to crustaceans , to reptiles and amphibians. if it is floating in the water and can fit in their mouth they will generally eat it.
obviously u are doing something wrong unless u have gotten all ur arowana stock from the same guy and he is selling bad (genetically or something) arowana. next time u attempt to keep an aro i would say be extremely precise with everything u do
get the right sized tank (gallon and foot print) if not already in ur posesion
drip acclimate the fish (if the pet store water quality is bad and the fish is put in water of high quality it can shock the fish)
do a proper quarantine treate for internal paresites and gill flukes
keep water at 83˚F, when u do water changes match temperature.
keep pH steady
do not over feed just feed small amouts 3 times a day, vary the diet crickets, shrimp, bloodworms, nightcrawlers, shinner, silver side, pellets (do not feed store bought live feeders)
keep water clean. i would say start with a bare bottom tank. do many smaller water chagnes in the week(20%-30% x 3) instead of one big water changen(50%-60% X 1) per week. vacum the poop each water change
test water quality regularly
now i have never had an arowana so i do not know from experience. however if anyone is having the same problem as u with any fish these are the steps to follow, obviously the water perameters should be changed accordingly.
if after doing this u still can't keep an arowana alive or u are not willing to do these steps i would just say forget about keeping an arowana.