The Asian redtail in my opinion are a little misunderstood. Out of the ten or so I have kept and grown on from small, only one has been truly nasty. By that I mean actively attacking other fish for no reason. Most will attack other hemibagrus and some will not tolerate other catfish similar to themselves but many will, in a large enough tank with many hideouts, live with other fish quite happily at this size. Obviouksly they will continue to grow and will need larger accommodation in time. You will also find that as the fish grows, more and more of that tank becomes his until eventually he sees the whole thing as his territory, that’s just natural and means the tank is not big enough.
When he starts turning on others after being ok with them is an indication it’s time for a bigger tank.