I'm starting to wonder if the more space you give them the more territorial they are. I had 2 Dorado in my 300 and they relentlessly chased eachother. Now I have 5 in a 40 and they are perfectly fine and have been for months. Tankmates are an absolute must if you ask me. If they won't tolerate other fish they probobly aren't going to tolerate eachother. Disperse the aggresion by not letting them focus the aggresion on 1 fish. Having just a pair of fish allows no other outcome but all the aggresion directly on 1 another. Live and learn. Its only a waste if you don't learn anything from it. Don't let the "what ifs" get ya, you've become smarter, and knowledge is priceless.