Now I heard that if they are grouped appropriately and when breeding, they’re gonna have best colours and best not to get it for that tank. So now am confused.
Except for one lone female years ago, I've always kept kribs in pairs, so I don't know how they'd do in a group unless the tank was pretty good sized. Even in a good-sized tank, as soon as a pair develops I'll bet money that all the rest would be hiding in the corners and along the edges of the tank and would be so stressed they wouldn't stay healthy. I've never met a pair of substrate-spawning cichlids that didn't think that they owned the entire tank once they started breeding. Even angels and discus get territorial during spawning. You could keep a pair comfortably in your tank, and kribs usually aren't too picky about accepting mates picked out for them IME. The lone female I kept was the last young of one of my pairs. I couldn't find a home for her for nothing. I ended up putting her in a 20 gallon long with some congo tetras and something else, though I don't remember what that something was. Anyways, she lived in that tank for a long time, was healthy and happy, and was pretty enough, though she never attained full breeding colors.
Kribs aren't especially aggressive compared to Rift Valley, Central American, and some South American cichlids, especially the females. And the 3" figure for a female is the maximum size. Typically my females have always stopped growing closer to 2-1/2" or slightly larger. I've kept them in community tanks where the rest of the fish are too big or too fast to be bullied.
I think where the confusion is arising comes from the difference between "aggressive" and "predatory". They aren't the same. A fish can be non-aggressive against creatures that are too big to be prey. But when put in a tank that contains creatures that are naturally on it's menu, that fish's predatory instinct will kick in and it will hunt those other creatures. I doubt anybody here would say guppies are aggressive, but they'll still become predatory on their own young. Kribs are still opportunistic carnivores and I wouldn't keep them with any fish small enough to possibly be on the menu, and like I said before, I wouldn't recommend keeping them with any inverts.
That blows my mind about the convicts and the Gabon shrimp. I've fed full grown marmorkrebs at 3-1/2" or so with pincers attached to single or pairs of full grown convicts and the crayfish lasted all of about 20 seconds. It amazes me the convicts didn't hunt your Gabon shrimp down.
WYite