So, your water is too hard for discus, you haven't got the money for Uarus, and you're tight on tank space but would still like to breed some "odd" neotropical cichlid? An in and out favorite of mine and the aquarium trade may be just the ticket for you; the Festivum or Flag Cichlid, Mesonauta festivus. Doesn't get too big, not too nasty (unless spawning in a too-small system), and accepts all types of foods, and most types of water...
Festivums on Parade!:
All told there are five species currently recognized in the genus Mesonauta... however, the long-standing "Cichlasoma" (old genus name) festivum is the only member found in the trade.
Though some folks have had success keeping, even breeding festivums in systems as small as twenty gallons, it is strongly advised that you provide at least twice this gallonage (40) to provide space for occasional "spats" as well as overall stability.
This is a shy species that appreciates low intensity lighting and good decor/cover, preferably employing either live or realistic long-stem plastic plants (Echinodorus/swords, Vallisnerias, tall Sagittarias...), as well as situating their tank in an area of not great outside movement, preferably in a setting where they can see you coming.
Water chemistry is not overly critical. This species lives in water that is of a wide pH range (6.0 to 8.0) and temperature (25-34 C.) in the wild, but prefers softer, less hard water conditions (4-6 in the wild, under 10 in captivity). As with their common monikered discus kin, keeping metabolites to a minimum is a definite plus. There should never be detectible ammonia or nitrite and nitrates should stay within single digit range.
Another common name for the Flag Cichlid is "the poor man's discus"... and they are quite alike in their temperament, and compatibility with other fishes. As with most fishes, it's best to start your festivums small, in the one to two inch overall length, and have them "grow up" with their tankmates. When small, freshwater angels (Pterophyllum), larger gourami species, medium to larger barbs and other minnows and such are fine with them. As larger, more full-size specimens, other South American cichlids and some Central Americans like Severums, Juraparoids (Eartheaters), and Uarus, as well as larger callichthyid and smaller pimelodid catfishes, as well as tropical loricariids make fine choices.
Can festivums be kept with live plants? Sometimes... Flags can go either way in terms of planted tanks, tearing them up at times, but in most settings, individuals rarely do much damage.
Festivums will accept all foods, fresh, frozen/defrosted and prepared, but prefer the first two categories over dried, pelleted, flake foods.
These cichlids are amongst the hardiest of aquarium specimens. Though they can contract parasitic disease, they will be amongst the last to succumb to these pathogens, as well as environmental and nutritional insults. Should they develop biological disease, Festivums are easily treated with the typical aquarium remedies.
Flag cichlids are not difficult to sex, pair or breed. Males are larger, with the usual (for neotropical cichlids) longer, more pointed dorsal and anal fins, as well as prominently larger pectoral fins (see images here), and slimmer, more pointed spawning tube during the act itself. Pair bonds are formed when fishes are about a year of age and approximately four inches (ten centimeters) in length.
Like most other neotropical cichlids festivums spawn on a solid surface, usually a real or fake plant leaf or solid object and care for their young (a couple or more hundred depending on the size of the parents) for about five days duration till the young are free-swimming.
There is some evidence that parental care and protection of young are spurred by the presence of "dither fish"... other species present. These "extra" fish/es should be smart enough to stay away, and not too much larger, meaner than the Flag cichlids they're in with.
So... have you got clean water, a subdued lit, perhaps well-planted tank with an empty spot for medium sized shy fish? Do consider Flag cichlids as a possibility. They are reclusive, but hardy, low-demand specimens, especially as far as their family goes.
Leibel, Wayne S. 1993. A Fishkeeper's Guide to South American Cichlids. A splendid survey of this attractive and diverse group of freshwater tropical fishes. Tetra Press, Blacksburg, VA.
Loiselle, Paul V. 1985. The Cichlid Aquarium. Tetra Press, Melle Germany.
Mills, Dick. 1987. A truly festive season! FAMA 12/87.
Quinn, John R. 1987. Notes on Cichlasoma festivum, "the poor man's discus". TFH 1/87.