Angelfish care

Tank size: not a 20-gallon fish

Most beginners encounter angelfish in pet-store community-tank displays, often labeled as a 20-gallon fish. The 20-gallon recommendation is for juveniles only — fish that will outgrow the tank in 6–12 months. The body alone reaches 6 inches; the trailing top and bottom fins add another 2–3 inches. Adult angelfish need vertical swim space the 20-gallon doesn't provide.

Realistic minimums by setup:

• Solo angelfish: 29 gallons with at least 18-inch height. Tank height matters more than length for angelfish — they swim vertically more than most fish.
• Pair (breeding or non-breeding): 55+ gallons. Pairs become territorial; the second fish needs space to escape the dominant one when tensions rise.
• Community of juveniles:75+ gallons if you're keeping 5–6 juveniles long-term. As they mature and pair off (usually 2–3 will pair from the group), the unpaired ones get harassed unless there's genuine room to escape.

Water parameters

Wild-type angelfish come from soft, slightly acidic Amazon tributaries. Tank-bred stock (which is what virtually all commercial angelfish are) tolerates a wider parameter range but still has firm targets:

• Temperature: 78–84°F (25.5–29°C). Warmer than community tanks. A heater is essential.
• pH: 6.5–7.5. Slightly acidic to neutral.
• GH: 5–13 dGH. Tolerant.
• KH: 3–8 dKH. Stable buffering matters.
• Ammonia / nitrite: 0 ppm sustained.
• Nitrate:< 20 ppm. Sustained higher nitrate is the leading suspected cause of HITH.

Water-change cadence: 25% weekly is the standard. Angelfish are not particularly sensitive to water-change rhythm but they do notice missed cycles, and nitrate accumulation is the avoidable factor in their most common chronic disease.

Tank mates: predator math first

The first rule of angelfish tank mates: any fish small enough to fit in an adult angelfish's mouth is potentially food. Angelfish mouths gape larger than they look. The classic beginner mistake is stocking a planted 55-gallon with neon tetras and a young angelfish, then watching the neon population gradually disappear over 6–12 months.

Compatible (with caveats):

• Larger tetras — rummy nose, lemon, black skirt, congo. Body height too tall for the angelfish to swallow.
• Cardinal tetras (borderline) — slightly larger than neons, often safe but not guaranteed
• Corydoras catfish — bottom-dwellers, ignored by mid-water angelfish
• Otocinclus — too small to chew but stick to algae surfaces; usually fine
• Bolivian rams— same parameter range, peaceful cichlid neighbors that don't compete for territory
• Discus — natural co-habitants in the wild; require warmer water and pristine quality, advanced-only setup

Avoid:

• Neon tetras / ember tetras / chili rasboras — small enough to be eaten, especially when angelfish reach adult size
• Tiger barbs / serpae tetras— known fin-nippers; angelfish's long trailing fins are a target
• Other large cichlids — territorial conflict in anything but very large tanks
• Guppies — flowing fins trigger angelfish to attack; juvenile guppies become snacks
• Adult shrimp — eaten as snacks; stick to cherry shrimp colonies that breed faster than angelfish can consume them, or skip

Diet

Angelfish are carnivorous-leaning omnivores in the wild — small insects, fish fry, and some plant matter. In captivity:

• Staple: high-quality cichlid pellet or flake (Hikari Cichlid Gold, Omega One Cichlid). Sized for medium-mouth cichlids.
• Variety 2–3× weekly: frozen bloodworms, brine shrimp, daphnia. Helps prevent the dietary monotony that contributes to HITH.
• Occasional live foods (mosquito larvae, blackworms) stimulate natural hunting behavior; not necessary but beneficial.
• Skip one feeding day per week. Angelfish overeat readily and constipation triggers more health complaints than under-feeding.

Common health issues

• Hexamita / hole-in-the-head (HITH).Pits on the head and along the lateral line; loss of color in surrounding tissue. Causes are multifactorial — sustained high nitrate (>40 ppm), nutritional deficiencies, and protozoan parasites are all implicated. Treatment: metronidazole-medicated food (Seachem Metroplex mixed with frozen bloodworms is standard) for 1–2 weeks, plus aggressive water-change schedule and a more varied diet. Catch early; advanced HITH is harder to reverse.
• Fin rot. Trailing fins damaged by fin-nipping tank mates or poor water quality. Fix the tank-mate issue (or water issue), treat with aquarium salt or methylene blue if advanced.
• Ich. White spots like grains of salt. Common after temperature drops or new fish introductions. Raise tank temp to 86°F for 10 days; treat with ich medication if persistent.
• Internal parasites. Wild-caught and some tank-bred lines arrive with internal parasites. Signs: weight loss despite eating, white stringy feces. Treatment: praziquantel or metronidazole (depending on parasite type) per package directions.
• Bullying within a community.Adult pairs will harass any angelfish that doesn't pair off. Resolution: remove the unpaired fish to a separate tank, or have enough tank space (75+ gal) for genuine territory separation.

Where hobbyists disagree

• Tank size for a pair. Some references say 29 gallons is enough for two; the modern consensus has shifted to 55+ gallons. The conservative beginner-safe answer is 55+ for anything beyond a juvenile pair.
• Mixing with small tetras. Some keepers report successful neon + angelfish setups when raised together; others consistently lose tetras. The variability is real, and the beginner-safe answer is to skip the combination — too many failed attempts among new keepers.
• Wild-caught Altum vs commercial Scalare. Pterophyllum altum(the rarer wild-caught species) is substantially more demanding — softer water, warmer temperatures, specific dietary needs. Commercial "angelfish" are almost always P. scalare; if a seller has Altums, that's a different species with different requirements and not what this guide covers.
• Hexamita as a parasitic vs nutritional disease. Treating with metronidazole alone often produces incomplete results — the prevailing modern view is that HITH is multifactorial (parasite + diet + nitrate stress) and requires addressing all three. Older sources frame it as a pure parasitic disease.

Frequently asked questions

What size tank do angelfish actually need?

29 gallons is the realistic minimum for a single adult, with at least 18 inches of vertical height — angelfish are tall fish that grow to ~6 inches body length plus trailing fins. A breeding pair needs 55+ gallons because of territorial behavior; a community of 5–6 juveniles that may eventually pair off needs 75+ gallons. The 20-gallon tank ads you'll see angelfish marketed at are appropriate only for juveniles you're planning to upgrade.

Will angelfish eat my neon tetras?

Often, yes. Adult angelfish will eat any fish small enough to fit in their mouths, and neon tetras are squarely in that range. Some keepers report mixed angelfish + neon setups working when raised together from juveniles — the angelfish learn to tolerate the tetras as tank mates rather than food. But the reliable beginner-safe answer is to skip the combination. Larger tetras (rummy nose, lemon, black skirt) are safer.

What is hole-in-the-head disease?

Hole-in-the-head (HITH), also called hexamita or head and lateral line erosion (HLLE), is a chronic disease that produces small pits on the angelfish's head and lateral line. Causes are debated — the leading theories involve sustained high nitrate (>40 ppm), poor diet, and protozoan parasites (Hexamita / Spironucleus). Treatment combines metronidazole, water-quality improvement, and a higher-variety diet. Prevention is reliable: keep nitrate under 20 ppm, feed varied foods, don't ignore early symptoms.

Can I keep just one angelfish?

Yes. A single angelfish is comfortable and often less aggressive than a pair (no breeding territoriality). Some hobbyists insist angelfish need a partner; established hobby consensus is solos do fine if other tank mates are appropriate. The downside of a solo is no breeding behavior, which is genuinely interesting to watch when it happens.

What temperature do angelfish need?

78–84°F is the consensus range, warmer than most community tanks. This is one reason angelfish don't pair well with neon tetras (72–78°F) — the temperature compromise is on the high side for neons and on the low side for angelfish. They share well with cardinal tetras (76–82°F), discus (which want even warmer), and Bolivian rams. The heater calculator handles wattage for the warmer target.

Related

• Tank volume calculator — verify your tank actually holds 29+ gallons (or 55+ for a pair).
• Heater sizing — wattage for the warmer 78–84°F target.
• Water parameters explained — the nitrate management discipline that prevents HITH.
• 55-gallon planted setup — the realistic minimum tank for a pair, ideally planted.
• Cycling a new aquarium — non-negotiable before adding any angelfish.

Sources: FishBase (Pterophyllum scalare species page), Aquarium Co-Op care references, peer-reviewed literature on Hexamita / Spironucleus in cichlids (Paull & Matthews 2001; Sterud et al. 1998), and mainstream hobby consensus on angelfish stocking. Where sources diverged, this guide takes the conservative beginner-safe position.