i just added another red to my four, they are all the same size but they have been attacking the new guy. Will this eventually go away or will they kill him? The four have been together for about 3 weeks. They are all about 3.5 inches.
You have introduced a new guy to the established territories. This is trouble. You need to remove all 4, rearrange you decor and then add them all at the same time. And you need to do it now or your new guy might not make it.
yes definately rearange a tank when adding fish that are territorial changing the way the decor was set out will make them look for new territories ,i did this when adding 3'' reds with 7'' reds and had no problems at all