I wouldn't suggest cichlids of any variety in a Hex. Ciclids need -space- to establish territories, and the wider and longer your tank, the more room fish have, the less aggression you will have. Very few fish are actual verticle swimmers the way a hex is designed, and cichlids are definately in need of wider space over gallonage when stocking levels are concerned. Some cichlids also grow -large- and the narrow confinds of a hex wouldn't allow a 10" fish room to manuver.
I wouldn't reccomend adding all the cichlids all at once unless your tank has been completely cycled. While two pair of certain SA cichlids are all that could be stocked in a 42 gallon tank, to add them all at once will most certainly ammonia spike your tank unless you have it compeletly cycled. There is an article on how to fishless cycle a tank on this website. But even then, you would want to add fish slowly to "test the waters" so to speak. Even in a cycled tank, ammonia spikes can occure from overpopulation all at once.
The knack to stocking cichlids is that, if you have a population in the tank already, and wish to introduce another fish to the tank, you must -rearrange- all your decor. Cichilds are territorial, and will fight amongst each other until the pecking order and territories are established. This pecking order will remain relatively stable unless a fish is removed or a new fish is added. It is always a good idea to add two or three cichlids together so that the aggression of the existing population is not focused on -one- newcommer, and to rearrange the decor so as all the fish are fighting each other for the establishment of new territories, thus diffusing the aggression still more so it is not just the newcommers trying to fight it out for themselves. Territory holders are more likely to be stronger and healthier than "invaders" so making everybody fight over "new" territory evens the playing field. Eventually a new pecking order and territories would be established and the fish will settle down again, the newcommers acting as if they've always been there.
With the hex you have, I would stick to smaller community fish such as tetras and corries, so that the tank is "large" relative to the fish, giving the fish more room to manuver. Just because you have a whole lot of gallonage doesn't mean you can have "big" territorial fish like cichlids. I've seen some 36" tall tanks that were only 12" wide, and the 10" fish in them were very uncomfortable even though the volume of water could support them. Besides, tall tanks have circulation and lack of oxygen problems without lots of filtration to move water off the bottom for O2 exchange at the surface.
~~Colesea
