I have had a pair of kribs for a little over 3 months, and I have been nothing but delighted with them. Although they can be quite territorial, they are generally peaceful and always very interesting to watch. I would not recommend these fish for the beginner as they are quite sensitive to water quality and conditions.
I purchased two female Kribs purely for the enjoyment of their colours. They seemed friendly to each other until, a week later, low and behold one had almost lost its entire tail fin. I nearly put her out of her misery. However, at last minute I decided not to, I left her alone in the 40 L Hospital tank, placed some medication in for reducing stress and preventing tail rot. In one month the tail grew back and she now resides in the 250 L with her sister. She has a permanent home until she dies regardless. The two sisters now have their own territories, one at each end of the tank. All is forgiven.
Kribs, at least in Australia, can be aggressive. Don Stevenson said in an earlier comment that he keeps his with cardinal tetras. Gotta say that my experience with neon tetras has been that they make a very nice snack for a krib. When I caught my new krib with a tetra hanging out of his mouth, my first reaction was anger. The guy in the fish shop said Kribs and Neons would get on great. I removed the little corpse from his mouth (forcibly) and then put him in another tank with some of my bigger rainbowfish to cool off. My disappointment in him subsided after a while and eventually I put him back with my glowlites, neons, gold neons and emerald eye rasbora's, but sure enough the neons semed to keep on slowly disappearing overnight (at least he was kind enough to eat the fish at night to spare me the grisly details). Eventually he made his way back to the LFS. Generally an awesome fish. Beautiful, amazingly maneuverable (they can swim just about any direction) and interesting to watch, but careful if you have little guys around.
Great fish, but they can be aggressive. I have a male and a female krib, but they're too young to spawn yet. My kribs seem to hate fish with long fins, or any kind of fish that likes to show off. They killed my fighter (betta), as well as half a dozen other fish. I love my little killers.
Kribensis are truly majestic fish. I have owned mine for around a year now and have had learned to love their charismatic, brave personalities which occasionally lead to them taking on a fish that is more than they can handle. I had to leave my 9 cm male with a friend while we went on vacation, feeling very nervous after I learned what it would have to put up with over the next two weeks...a 20 cm oscar. When I returned I found my little mate in a breeding trap which was hooked on the side of my friends 200 L aquarium. Apparently the oscar was being so aggressive that their was nothing else that could be done. Not all kribensis are those tough little nuggets that some fish keepers say could take on a full grown green terror! Even though books etc, say that kribs like water that is around 6.7-6.8. This is not how they are kept in pet shops. They become acclimatised to a neutral pH. You should definitely take this site's advice when keeping kribensis. Aquarists buy a striking looking fish, only to find that after they place the fish in their acidic water that they have lost their colour. This is a common mistake, one that I made for many years. Kribensis bully and may even kill slow moving catfish like bristlenoses. However there is an exception in the clown loach which I have found to be an excellent companion for kribensis. Kribensis are not supposed to spend all of their time in a pot (even though this is natural behaviour). This is usually a result of minimal planting or a lack of courage as I like to say. Planting the aquarium heavily and adding some peaceful species that swim in the high strata of the tank usually solves this; there are however some unexplainable exceptions.
I have had my kribensis for just over three years now, having been given a pair by a friend's friend who was moving out of state. I have found them to be a rather hardy fish, saying they were able to survive a quick acclimation process and unmonitored adaption to my 100 L tank (I went on vacation immediately after being given them). At first they got along well with the other fish in the tank, but soon I found them too robust for the tankmates in the 100 L, so they were moved downstairs to the 200 L I had received with them. Downstairs they shared a tank with the gifted guppies, gifted Chinese algae eaters, and gifted clown loaches. I managed to get my kribs to spawn twice, but both times the babies were eaten, assumedly by the loaches. About six months ago my male krib vanished, to this day I'm yet to find his body. One assumes he was killed by his mate, no other fish in the tank was capable of killing him. (He was about 7 cm long at the time). I took down the 200 L and moved the female (and the few remaining fish) to the mostly empty 100 L. I find her to be a very gentle cichlid, she only pesters the cherry barbs when they come too near her cave. All in all, I highly reccommend this fish to anyone who wants a fun cichlid, who is relatively peaceful. She's about 5 cm.