I have a 40 gallon breeder that has a good amount of rockwork and good filtration, the current stock list is 2 yellow labs, one red zebra, on kenyi (he is very sweet and not agressive), and a albino lab. They are all about a inch or so, one of the labs is a little bit bigger, since he is dominant in the tank he has grown faster. I was wondering if it would be much of a problem adding another mbuna, i was thinking yellowtail acei or another more peaceful kind, but not another of one i currently have, will i run into problems a year so so from now? earlier, later?