Agree... This is good advice. *If you have the filtration to hande the bio-load* you need to add more fish and add cover in the form of rock caves. You need to break up the line of site. A picked on fish needs a place to retreat to, so they can get out of site long enough for the bully to find someone else who is a threat to his territory. There will always be an established pecking order in your tank and, actually, that is what keeps your tank stable. however, if you don't have enough cover for your fish, the bully will just constantly chase the weakest of the fish until they are dead. Then he will start on the next weakest and so on.
Flat rock works well to build caves with. Use small pieces for the vertical and large pieces for the horizontal and build them up several layers like apartment buildings. Be careful, take your time and make them very stable so as not to risk them falling into your tank walls.
Best of luck...
As keeper's of ANY animal we assume & bare by choice the ultimate responsibility to our domesticated friends. There's no reason especially in the tech age we live in (prior to this we had to get info thru good old publication's, see Dr. Brichard's & Ad Konning's numerous publication's) to not be able to inform ourselves. It's unfortunate that you would have to learn this lesson this way, but I bet/hope you won't make a mistake like this again. I really hope you don't give in, give up & move to something less challaging, because the true reward's are found in the face of adversity. Don't mean to kick anyone when their dwn, but it stands as a lesson learned the hard way for all new comer's looking to educate themselve's. Good luck w/ the goldfish
