OATA gives at least 120 liters (31.7 gallons) for a pair of the smaller American cichlids, under 15 cm, a group that includes angelfish, and 300 liters (79.3 gallons) for larger ones. Angelfish also need a heater and a tank tall enough for them full grown.
How many
Your tank
Your tank against each minimum
What to get
What to get
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A pair or a group
Angelfish are social, and OATA says to keep them in groups or a pair at minimum. For each adult past the pair, OATA allows another 40 liters (10.6 gallons).
A second view: a hobby database
aqua-fish.net, a hobby fish database, gives the angelfish (Pterophyllum scalare) a well-planted tank of at least 100 liters (26.4 gallons) for a small group, and prefers bigger for its tall fins. That’s less than OATA’s 120 liters for a pair, so OATA’s figure is the safe side.
Angelfish by source
Source
Tank
Water
pH
OATA (American cichlids)
120 liters for a pair, plus 40 liters per adult past it
22–27 °C
6.5–8.0
aqua-fish.net (hobby database)
100 liters for a small group
23–29 °C (73.4–84.2 °F)
5.3–7.6
aqua-fish.net puts the usual size in a tank at 12 to 15 cm (4.7 to 5.9 in), and asks for gentle filtration and regular water changes. It calls angelfish generally peaceful, though they may turn a little territorial when breeding, and omnivores: good flakes or pellets with live or frozen foods such as bloodworms, tubifex or brine shrimp.
Tank mates
OATA says calmer species like angelfish and severums can be mixed in a robust community aquarium with larger shoaling species.
OATA’s sheet covers American cichlids as a group, and its temperature and pH are for the whole group. It says to check with your aquatic shop for any species-specific needs.
Common questions
How many angelfish can go in a 55 gallon tank?
Four adults, by OATA's figures: 120 liters for a pair plus 40 for each adult past it comes to 200 liters for four, and a 55 gallon tank holds about 208.
Can I keep a single angelfish?
OATA advises against it: angelfish should be kept in a pair or a group, because one kept on its own may become stressed.
How big do angelfish get?
aqua-fish.net, a hobby fish database, gives 12 to 15 cm (4.7 to 5.9 in) as the usual size in a tank. OATA's 120 liters is for a pair of American cichlids under 15 cm.
Care and tank sizes come from OATA’s American cichlid sheet, which includes angelfish, with notes from RSPCA, a second view from aqua-fish.net (a hobby fish database), and filter flow from Aqueon. Checked against published data from RSPCA, NIST, OATA, Aqueon and aqua-fish.net.
RSPCA, Ornamental fish: Environment (“Choosing an aquarium”)
RSPCA, Ornamental fish: Diet
OATA, How to care for American cichlids (includes angelfish), September 2022 (PDF)
Aqueon, “How to Choose the Best Filter for You and Your Tank” (maker article)
aqua-fish.net (hobby fish database), Angelfish, Pterophyllum scalare
General care guidance from animal welfare charities, vets and makers' published sizes. It isn't veterinary advice: if your pet seems unwell or has eaten something it shouldn't, call your vet.