Cockatoo dwarfs, like most dwarf cichlids, are bottom-oriented. This means the footprint of the tank is much more important to them than the overall water-holding capacity. A long, low tank is preferable to a high or display-type tank. In other words, a 20-gallon (76-liter) long is preferable to a 20 high, and a 30-gallon (113-liter) long or 33-gallon (125-liter) extra long is preferable to a 29-gallon (110-liter). A “breeder” style tank would be even better. My favorite tank for a group of cockatoos is a 30- or 40-gallon (113- or 151-liter) breeder.
Cover the bottom with a thin layer of fine gravel or even sand. Add a couple of pieces of driftwood with epiphytic plants like Anubias or Java fern attached, a couple of caves (new ceramic or plastic flower pots or even coconut shells with a hole cut in them), and a clump of Java moss.
Choose whichever filter you prefer, as you are more likely to service one that you like and are comfortable with. I use sponge filters or mattenfilters in all of my tanks, even my 125- and 135-gallon (473- and 511-liter).
As I mentioned earlier, there is no need for a heater as long as the room temperature doesn’t go below 60°F (15°C) for any length of time. If you absolutely have to have a heater, set it for 72° to 74°F (22° to 23°C).
As said before, your local water is probably fine for the very-adaptable cockatoo apisto. Instead of focusing on hitting an exact pH or hardness number, realize that in the wild, these numbers fluctuate throughout the year and hitting an exact number isn’t that important for cacatuoides. What is important is to do large, regular water changes to keep dissolved organic compounds and nitrogenous wastes in check.
I like to do a 50-percent water change every week to 10 days, though with my travel schedule, that sometimes stretches out to once every 30 days. But with just eight cacatuoides and some small livebearers as dithers in the tank, the bioload is very light and doesn’t build up very quickly in a 40-gallon (151-liter) breeder.
A. cacatuoides is not very picky when it comes to foods. I feed live foods every day, but I also feed flakes, pellets, and frozen foods several times a week to give them a varied diet. They take every food I add to the tank.
In order to bring them into breeding condition, I feed them live worms several times a week. I currently use live blackworms and chopped earthworms, but Grindal worms and white worms will work, too. They will also take daphnia, live adult brine shrimp, and small cherry shrimp. Surprisingly, even adults will take newly hatched brine shrimp.
They are also miniature eartheaters, especially the males. They spend much of their time digging into the sand, sometimes up to their eyes, looking for food. They’ll pop up with a mouthful of sand, move it around their mouth, and carefully squirt it out through their gills, extracting any food items as they find them.
Whenever fry are present in the tank, I always squirt newly hatched brine shrimp and microworms into the tank near the fry at least twice a day. The fry will also graze on the surfaces of the plants, nibbling at the nutritious biofilm (aufwuchs) that grows there.
The cockatoo apisto is a cave spawner. You should always keep at least as many caves as there are females in the tank. I like to add a couple extras just in case. The openings should not face one another, and the caves should be staggered around the tank with other dÉcor in between to break up the line of sight and give each female some privacy.
The males will fight amongst themselves until one establishes his dominance. He will be the breeder. The other males likely won’t get a chance to breed and will likely be beaten up each time they venture into the open in sight of the dominant male. It is easy to tell which male is dominant—he will be out in the open, in full color, courting the females. Usually he won’t have any torn fins.
The sub-dominant males will take on a pale coloration, keep their dorsal fins clamped, and stay on the lookout for an escape route. For the sake of the fish, the sub-dominant males should be removed unless the tank is heavily planted and rather large (over 75 gallons [284 liters]).