I created a very simple blaze farm. I set up a ring of portals around the farm so that when they spawn they only have a 3x3 area to move around in. When their AI makes them walk into the portal they end up in an area where I can have pistons suffocate them to 1 heart. In theory it works. With a small amount of blazes it works. But when there are a large number of blazes in the farm they end up shooting fireballs at each other and killing each of so that I can't get any rods or xp (I throw harming potions at them). Any help would be appreciated.
Are you triggering them to try to attack you? A way to prevent this happening is to only have air blocks at their feet, so the blazes see a solid block in front of them.
CLICK THEM OR THEY DIE
CLICK THEM OR THEY DIE
When blazes see a player, or get punched, they flare up, fight and kill each other.
The trick is to assure they never see a player and "soften" them to one hit before trying to kill them.