Discus
Amazon cichlids that feed their fry on a secretion from their own skin for the first weeks. They want warm soft water and quiet company.
Overview
Discus are tall, disc shaped cichlids from the lower Amazon, recorded to 13.7 cm, and they live in deep, rocky water among roots and crevices. FishBase describes them as normally schooling but territorial while breeding, and sets the minimum aquarium at 120 cm, about 55 gallons.
They have a reputation for being difficult. Most of that comes down to warmth and consistency rather than anything exotic: they want water at the high end of tropical, and they react badly to it moving around.
Temperament
Calm, slow moving and easily unsettled. Discus startle at sudden movement outside the glass, and a tank in a busy corridor will show it in fish that hang at the back.
They do best in a group of five or more, where the pecking order spreads out. In a group of two or three, one fish usually takes the pressure. During breeding a pair turns territorial and holds a patch of the tank, which is a marked change from how they behave the rest of the year.
Care and grooming
Insect larvae, insects and planktonic invertebrates in the wild, so frozen food and a quality pellet in a tank, fed several times a day for young fish.
Heat is the defining requirement. FishBase gives 26 to 30 degrees C, which is 79 to 86 F, warmer than most community fish want, and the pH range runs 5.0 to 8.0 with soft water preferred. Frequent water changes are the norm in discus keeping because the fish are fed heavily and the tank is warm, which is exactly the combination that loads a filter.
Living and exercise
A tall tank, at least 120 cm long, planted or set up with driftwood and roots. Height matters for the same reason it does with angelfish: the body is deep, and a shallow tank crowds it.
Tank mates are chosen for warmth tolerance first. Most community fish are uncomfortable at 86 F, so the usual companions are cardinal tetras and corydoras species that share the range. Boisterous or nippy fish are a poor match for something this deliberate.
Something here wrong or out of date?