You need to cycle the tank.
Get the tank all set up with the sand/gravel, decorations, filter, heater, etc. Because your Arawana is so large, he represents a rather large bioload, to get the bacteria in the tank ready to support him, you need to build up thier population. You can get a head start on this by transfering something from the old tank for your starter culture. Then you need to feed the bacteria. There are two popular methods: raw seafood, and normal fish food. I personally prefer the fish food method, because you already know how much your arawana eats, so you can put an equivilant amount of food into the empty tank, to represent the same bioload that the fish itself represents. (If you normally put in live food, you need to put in an equivilant in dead food.)
Next, get test kits for ammonia, nitrite, and nitrate. After you start putting food in the tank, ammonia will spike first, then as it comes down, nitrite will spike. (If ammonia goes above 4.0, skip a feeding, it has more food than it can process.) When nitrite starts to come down, nitrate will go up. You need to keep feeding the tank until ammonia and nitrite are 0, and nitrate has gone up. (5-40
ppm Nitrate is normal after a cycle.) At this point the tank should be ready to support your arawana.
Test kits: Some people will tell you to get the more expensive, more precise test kits, but I think that for the purpose of cycling when you need to test every day, but don't care too much about the exact numbers, the quick dip test strips are great.