They develop the black spot on the base of the pectoral fin when they are mature, so if someone has an established group with black spots then it would be logical that they can be kept together but if no-one can confirm it then the jury is out.Are Black Axil Chromis (a more colorful Blue-Green Reef Chromis) - any better...?
So which species do you think you had when they were killing each other and what species do you have now they are not. Logically since you put them in the same tank with the same decoration the only thing that has changed is the fish.I have had problems with aggressive behavior from green cromis . I’d get 4 then there’s 3 , 2 , and 1 . This happened every time. But lately I bought from live aqua. I got 4 talbot demsels,2 kupang demsels, 1 springer demsel, and a lemon cromis . That night my aquarium was a battle royal . In a couple days everything calmed down. Fast forward 2-3 months and I’m not loseing any more green cromis .
My opinion is 2-6 green cromis will kill each other off . The same greencromis in a aquarium with say 15 other fish ( demsels ) and they cool off with aggression.
BTW I like demsels and cromis yes they are nasty, but they are 100% reef safe , colorful , cheep , and school , and are active , eat anything, and are hardy and healthy.
The one up at the front is definitely a black axel chromis. I can’t see enough detail on the others to tell if they are the same.
Not sure the exact ID but all sold as blue/green chromis. They have been together for a couple of years. The 2 talbots have been in about 6 months, the 3 yellow tails about 7 months. They get along pretty well with a Tomini tang and a single clown. Lots of sleeping holes and lots of food.