Wait until it is a couple inches larger, then try again, for longer than 7 days if necessary.
For mine, I got it at the same size as yours, fed it krill until it was about 7" long, then starved it until it accepted pellets (which took about 2 and a half weeks), just fed it pellets for a few months, then started feeding it a combination of pellets and krill until it was about 22-23" long, and since then I have been feeding it tilapia fillets cut into half-dollar sized pieces three times a week, and pellets on the days that it doesn't get tilapia.
I'm not going to claim to be "properly housing" mine, as I have learned the hard way in the past year that a 225 gallon is not an ideal size for such a powerful and unpredictable fish, but I will say that you are wrong. First of all, the "massive problem" you are referring to is entirely cosmetic in most cases; DE does not have any affect on the arowana's health or its ability to "hunt" normally. And considering the nutritional value of pellets compared to many live or frozen foods, I don't see how anyone could effectively defend your argument.
Thanks for the information, I'll try to do this then. Its just that i don't want it to have drop eye and maintain in a good health.
