What Altum Angelfish Are and Why They're Different
Altum angelfish are a tall, silvery freshwater species native to the Rio Negro and upper Amazon basin in South America. They look similar to the common angelfish you see in most aquariums, but they grow taller and narrower, with longer dorsal and anal fins that extend almost to a point. An adult altum can reach 6 inches tall and 3.5 inches wide, making them noticeably larger and more angular than the standard angelfish most people keep.
The key difference between altum and common angelfish is not just size—it's temperament and water requirements. Altums are more sensitive to water conditions, more prone to stress, and more likely to develop disease if their environment shifts suddenly. They also cost significantly more, typically $15 to $40 per fish depending on size and source, compared to $3 to $8 for a common angelfish. This price difference reflects both their rarity in the hobby and the difficulty of breeding them in captivity.
If you're drawn to angelfish but have kept common ones before, altums are a step up in commitment. They reward careful attention with striking appearance and longer lifespans—often 8 to 10 years in a stable tank—but they will not tolerate the shortcuts that common angelfish sometimes survive.
Key Takeaways
- Altum angelfish require tanks at least 40 gallons and prefer water between 75 and 82 degrees Fahrenheit with a pH of 5.5 to 6.5, which is more acidic than most community tanks.
- They are sensitive to ammonia and nitrite spikes, so a mature filter and weekly water changes of 25 to 30 percent are essential, not optional.
- Altums are semi-aggressive and will eat small fish and shrimp, but they can coexist with larger tetras, peaceful cichlids, and bottom feeders if the tank is spacious enough.
- Breeding altums in captivity is difficult and rarely successful outside specialized breeding operations, so most fish sold are wild-caught imports.
- A single altum can live 8 to 10 years with proper care, making them a long-term commitment rather than a beginner fish.
Tank Size and Water Volume
Altum angelfish need more space than common angelfish because of their height and their need to move without stress. A single altum requires a minimum of 40 gallons, though 55 gallons is more realistic if you want the fish to display natural behavior. If you plan to keep a pair or a small group, add 20 gallons for each additional fish.
Tank shape matters as much as volume. Altums are tall fish, so a tank that is at least 18 inches high gives them room to display their fins and move vertically without feeling confined. A 40-gallon breeder tank (36 inches long, 18 inches wide, 18 inches tall) is better than a 40-gallon long tank (48 inches long, 12 inches wide, 16 inches tall) because the extra height reduces stress. Avoid tall, narrow tanks like 20-gallon high setups—they look spacious but leave altums nowhere to swim comfortably.
The tank should have gentle water flow and plenty of vertical space. Altums do not appreciate strong currents, so position your filter outlet to create a slow, even circulation rather than a jet. Live plants, driftwood, and tall decorations help break up the space and give the fish places to retreat, which reduces aggression and stress.
Water Temperature, pH, and Chemistry
Altum angelfish come from soft, acidic water in the Amazon, and they perform best when your tank mimics those conditions. The ideal range is 75 to 82 degrees Fahrenheit, with a pH between 5.5 and 6.5. This is significantly more acidic than the neutral 7.0 pH that common angelfish tolerate, and much more acidic than most community tank setups.
Achieving this pH requires either using reverse osmosis water, adding peat moss to your filter, or using commercial pH buffers designed for soft-water fish. Many aquarists use a combination: they start with tap water, add peat to lower the pH naturally over time, and use a buffer to stabilize it. Test your water weekly with a reliable kit—pH can drift, especially in new tanks, and altums become stressed and susceptible to disease when pH swings.
Water hardness should stay below 6 dGH (degrees of general hardness). If your tap water is hard, you will need to blend it with distilled or reverse osmosis water, or rely entirely on treated water. This is not a casual adjustment—it is a core part of keeping altums, and skipping it is the most common reason they sicken within weeks of purchase.
Filtration and Water Changes
Altums are sensitive to ammonia and nitrite, so your filter must be mature and reliable. A canister filter rated for 1.5 times your tank volume is a good baseline—for a 40-gallon tank, use a filter rated for 60 gallons. Sponge filters work well too, especially in planted tanks, because they provide gentle flow and do not create dead zones where waste accumulates.
Do not rely on the filter alone. Perform a 25 to 30 percent water change every week, even if your ammonia and nitrite readings are zero. Altums are prone to stress-related diseases like ich and fin rot when water quality drifts, and weekly changes prevent the buildup of organic compounds that filters do not remove. Use a gravel vacuum to remove debris from the substrate, and rinse your filter media in old tank water—never in tap water, which kills the beneficial bacteria.
Test your water regularly. At minimum, test ammonia, nitrite, and nitrate every two weeks. If you are new to keeping altums, test weekly for the first month to understand how your tank cycles and where problems might arise. A reliable liquid test kit (not strips) gives you the accuracy altums demand.
Feeding and Diet
Altum angelfish are carnivorous and will eat small fish, shrimp, and insects in the wild. In captivity, they thrive on a varied diet of high-quality flake food, small pellets, and frozen foods like bloodworms, brine shrimp, and daphnia. Feed them once or twice daily, offering only what they can eat in 2 to 3 minutes. Overfeeding fouls the water and leads to bloating and disease.
Rotate between different foods to provide balanced nutrition. A typical week might include quality flake food four days, frozen bloodworms two days, and a day of fasting to let their digestive system rest. Altums in good condition will have a rounded belly but not a distended one, and their colors will be bright and even.
Avoid feeding live fish unless you are certain they are disease-free. Feeder fish from pet stores often carry parasites and bacteria that can infect your altums. Frozen foods are safer and just as nutritious.
Temperament and Tank Mates
Altum angelfish are semi-aggressive, especially toward smaller fish and anything that resembles food. They will eat neon tetras, cardinal tetras, and small shrimp without hesitation. However, they coexist peacefully with larger tetras like black skirt tetras and serpae tetras, peaceful cichlids like rams and apistogramma, and bottom feeders like corydoras catfish and plecos.
A pair of altums may spawn, and when they do, they become highly aggressive toward other fish in the tank. If you see a pair forming—they will stay close together and begin cleaning a flat surface—be prepared to either move one fish or remove all other tank mates temporarily. Altum fry are difficult to raise, and most aquarists do not attempt breeding outside of specialized setups.
Avoid housing altums with aggressive fish like cichlids larger than 4 inches, bettas, or barbs. They are not aggressive enough to hold their own against true bullies, and the stress of constant conflict will sicken them. In a well-planted, spacious tank with peaceful companions, altums display their best colors and behavior.
Common Health Issues and Prevention
Altums are prone to ich (white spot disease), fin rot, and bacterial infections when stressed by poor water conditions or sudden changes. The best prevention is maintaining stable water parameters and performing regular water changes. If you notice white spots, clamped fins, or lethargy, do a 30 percent water change immediately and raise the temperature to 82 degrees Fahrenheit for a few days to speed up the ich lifecycle.
Parasites are common in wild-caught altums, especially internal parasites. Many aquarists treat new altums with a broad-spectrum antiparasitic medication as a precaution, following the product instructions carefully. Quarantine new fish in a separate tank for two to four weeks before adding them to your main display, so you can observe them for signs of disease and treat them without risking your established fish.
Stress is the root cause of most altum health problems. Avoid sudden temperature swings, pH changes, or tank mates that chase them. If an altum stops eating or hides constantly, check your water parameters first—disease is usually a symptom of poor conditions, not the cause.
Where Altums Come From and What to Expect
Most altum angelfish sold in the hobby are wild-caught from the Rio Negro and upper Amazon. They are collected by local fishermen, held in export facilities, and shipped to distributors and retailers. This process is stressful for the fish, and many do not survive the journey. When you buy an altum, you are getting a fish that has already endured significant stress, which is why acclimation and stable conditions are so critical in the first weeks.
Captive-bred altums exist but are rare and expensive, usually available only through specialized breeders or high-end aquarium shops. They tend to be healthier and more adaptable than wild-caught fish, but they cost $40 to $80 or more. If you find altums at a local shop, ask whether they are wild-caught or captive-bred, and how long they have been in the store. Fish that have been in the shop for several weeks have already survived the worst of the import stress and are safer to buy.
Expect a new altum to hide for the first few days and eat little or nothing. This is normal. Do not chase it around the tank or make sudden movements. Keep the lights dimmed, maintain stable water conditions, and offer small amounts of food. After a week, most altums begin to relax and show their true behavior and coloring.
Frequently Asked Questions
Can I keep altums in a community tank with common angelfish?
No. Altums and common angelfish have different water requirements—altums need acidic, soft water while common angelfish prefer neutral, harder water. Mixing them also risks aggression and disease transmission. Keep them in separate tanks.
How long do altums live?
Altums typically live 8 to 10 years in a well-maintained tank, sometimes longer. This makes them a long-term commitment. Poor water conditions and stress can cut their lifespan to 2 to 3 years.
Do altums need to be kept in groups?
No. A single altum does fine alone. A pair may spawn, but they will become aggressive toward other fish. Most aquarists keep one altum per tank unless they are specifically breeding.
What should I do if my altum stops eating?
Check your water parameters immediately—ammonia, nitrite, pH, and temperature. A sudden loss of appetite usually signals stress or poor conditions, not disease. Do a 30 percent water change and retest. If parameters are stable and the fish is still not eating after three days, consider quarantine and treatment for parasites.
Are altums harder to keep than common angelfish?
Yes. Altums require more precise water conditions, more frequent maintenance, and more careful acclimation. They are best suited to aquarists with experience keeping sensitive fish. If you are new to the hobby, start with common angelfish or other hardy species first.