any ammonia is bad! It means you have a problem somewhere in your filtration( or not enough) do a water change and get you ammonia in order. Also your nitrate is high. I try to keep mine around 10ppm which is considered low but the lower the better. Arowana's aren't overly hard to keep but they will be one of the first to act strange when something isn't right. I wouldn't crank your temp up if it's above 75f because warmer water holds less O2. It is sounding like you may be fighting a fungal infection but it's hard to tell without pics. You can add salt but do it gradually. start with a tablespoon for every 5 gallons and give it time to work