I would say part of the problem is substrate, and the other is that most cichlids don't look their best if they aren't top dog in the tank. I find it funny when people say you can't house that many fish in one tank. Just because you have a green terror doesn't mean that for you to bring it home from the pet store it has to go in a very large tank by itself. For all we know those fish could be tiny. All the fish in your tank are semi aggressive in my book. So, they'll tolerate each other longer then if you had Flowerhorns or red devils. The funny thing about cichlids is as soon as the tank is "over stocked" if you don't upgrade your tank, they will make room for themselves by killing each other.
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