Inirida F1 Altum Angelfish (Pterophyllum altum)

Decide whether this specialist Altum fits your aquarium

The Inirida F1 Altum Angelfish (Pterophyllum altum) is a freshwater South American cichlid from the upper Negro drainage and upper Orinoco tributaries, including the Inírida and Atabapo rivers. It reaches a recorded maximum total length of 18 cm. This is a fish for an advanced keeper who can provide warm, very soft, acidic water, a tall mature aquarium and measured stocking.

The FishBase account for Pterophyllum altum places it in the family Cichlidae, identifies it as a river-dwelling freshwater fish and gives 18 cm as its maximum total length. Plan every permanent decision around that adult figure, not around the compact proportions of a dispatch-size animal.

This is not the same species as the familiar Pterophyllum scalare. The Seriously Fish Altum profile describes demanding water chemistry, high temperatures, feeding challenges and sensitivity to nitrate accumulation and stress. Those combined requirements support our advanced care assessment. A well-prepared keeper gains a clear decision framework: establish the correct water first, choose sufficient height and capacity, mature the biological filter and screen every companion before adding the fish.

Check the decisive requirements together

Before choosing this fish, record the aquarium’s measured temperature, pH and general hardness, then confirm that all three sit within 28–31°C, pH 4.8–6.2 and 1–5 dGH. Check that the mature aquarium has sufficient height for extended fins and enough capacity for the planned pair or group. Finally, list every intended companion by adult size, water needs and feeding behaviour. A suitable result in one category cannot compensate for a conflict in another.

Choose the dispatch size without confusing it with adult size

One purchase supplies one Inirida F1 Altum Angelfish in the size selected on the live selector. The selector labels are 1.5-2 cm, 3-3.5 cm, 4-5 cm, 5-5.5 cm, 5.5-6 cm, 6-7 cm and XL. Choose by the aquarium space and feeding plan you can provide immediately, while retaining a permanent plan for an adult fish that reaches 18 cm.

The size you select is the size supplied, not the adult size. A dispatch measurement is not an age, sex or final-growth claim. Smaller fish still require the same long-term water chemistry, social planning and adult accommodation. An XL label is a dispatch grade rather than a numerical adult-size statement.

Sex is guaranteed only when the selected option explicitly states male or female. This Inirida F1 Altum Angelfish listing has no sex-guaranteed option. Seriously Fish describes this species as difficult to sex, with a male’s nuchal hump generally becoming apparent only around breeding time. Appearance in the gallery must therefore never be used to predict the sex supplied.

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal. Make the purchase decision from the written identity, selected dispatch size and care requirements.

The Inirida F1 wording identifies the named form on this page; routine care follows the requirements of Pterophyllum altum. Keep that distinction clear when comparing fish through our angelfish collection, because other angelfish species and forms must be assessed against their own adult size and water needs.

Plan the aquarium around adult growth and fin height

Plan at least 300 litres for this fish and choose an aquarium tall enough for an adult to hold its extended fins naturally. This volume is a planning minimum from OATA’s broad American-cichlid guidance for species over 15 cm, applied here because Pterophyllum altum reaches 18 cm. Aquarium shape matters alongside litres: a shallow vessel can hold considerable water while still giving a tall angelfish poor vertical clearance.

The OATA American-cichlid guidance recommends at least 300 litres for larger species and says angelfish need sufficient height when fully grown. It also gives 40 litres per adult fish as a stocking allowance for shoaling angelfish. Treat 300 litres as the starting point for a pair, then add 40 litres for every further adult angelfish and more room for any other fish.

Work through both space checks

• Adult-size check: Base the permanent aquarium on a fish reaching 18 cm, irrespective of its dispatch size.
• Capacity check: Begin with at least 300 litres because the species exceeds OATA’s 15 cm division between smaller and larger American cichlids.
• Stocking check: Add 40 litres for every adult angelfish beyond a pair, and buy the largest aquarium you reasonably can.
• Height check: Choose a shape that lets the fish swim and turn without its fins being constrained by the substrate, wood or surface.

FishBase also says the species may reach about 20 cm in height. Allow for that height as well as the 18 cm total length when choosing the aquarium. Leave open vertical corridors between the substrate and floating cover, and assess ornaments at the adult scale before the fish grows around them.

Hold the water inside the species range

Keep this Altum at 28–31°C, pH 4.8–6.2 and 1–5 dGH. These values are the overlap between FishBase’s 27–31°C, pH 4.8–6.2 and 1–5 dH environmental range and Seriously Fish’s aquarium range of 28–32°C, pH 4.8–6.2 and 0–5 dGH. Using the overlap keeps routine conditions inside both sets of species values.

OATA’s wider American-cichlid water table covers a diverse family and runs cooler, harder and more alkaline than the Altum ranges. For this animal, use the narrower values above. Seriously Fish says soft water with virtually undetectable hardness is mandatory and that the fish will not usually do well at all in less acidic conditions.

Make water matching a three-part decision

1. Measure first: Test the aquarium’s temperature, pH and general hardness rather than judging softness or acidity by appearance.
2. Compare all three values: A correct temperature does not compensate for hard or alkaline water, and a suitable pH does not compensate for a temperature below the stated range.
3. Prepare consistency: Use replacement water that keeps the aquarium within the same range during routine changes.

Our water-chemistry guide explains what the common aquarium tests measure. Enter measured results into the water matcher to compare them with 28–31°C, pH 4.8–6.2 and 1–5 dGH before committing livestock.

If any value falls outside the range, adjust the aquarium plan before introduction. Recheck after changes and again before the fish enters the aquarium. The goal is a repeatable routine that holds all three values together, not a single reading obtained immediately before purchase.

Build a calm layout with plants, roots and slow flow

Provide a densely planted, well-covered aquarium with floating plants, broad-leaved plants and root-like wood. Seriously Fish recommends this combination to dim the aquarium and reflect the branch-filled structure associated with the species’ river habitat. Keep enough open space for a tall fish to turn and move between pieces without brushing its extended fins.

Use sand or fine gravel as the substrate because Altums may dig. Check each piece of wood from the perspective of a deep-bodied adult: stable roots and overhanging branches should create cover without forming narrow traps. Place broad leaves and vertical wood around the edges of swimming routes rather than filling every route with decoration.

Arrange each feature for a purpose

• Floating cover: Softens the exposed upper area while leaving clear access to the surface.
• Broad leaves: Add sheltered structure around the middle and sides of the aquarium.
• Root-style wood: Creates overhanging branch forms and visual separation between areas.
• Fine substrate: Accommodates digging without relying on coarse material.
• Open vertical lanes: Give the adult body and fins room to pass between cover.

Keep water movement very slow. Seriously Fish associates the species with very slow-flowing rivers and specifically advises against a great amount of current. Filtration still has to process waste effectively, but position and adjust the return so the fish is not forced to swim continuously against a strong stream.

Observe how food and fish move after the system is running. If every meal is swept rapidly across the aquarium or the fish must work constantly to hold position, reduce or redirect the flow while preserving filtration. If debris settles heavily behind roots, remove it during maintenance rather than increasing the current beyond the species’ preference.

Mature the biological filter before adding the fish

Use a fully established biological filter and confirm ammonia and nitrite are both zero before introduction. The RSPCA aquarium guidance explains that fish release toxic ammonia, which filter bacteria convert first into toxic nitrite and then into safer nitrate. A filter is therefore part of the animal’s life-support system, not an optional device for making the water look clear.

Prepare and mature the aquarium before livestock enters it. Our first tropical aquarium guide gives the practical sequence for establishing the system. OATA advises adding fish slowly because every increase in fish and feeding requires the filter’s bacterial population to process more waste. Adding too much livestock too quickly can cause new tank syndrome, with ammonia and nitrite rising faster than the filter can manage.

Confirm these points before introduction

• Ammonia: Zero mg per litre.
• Nitrite: Zero mg per litre.
• Nitrate: No more than 20 mg per litre above the normal level in the tap water, following OATA’s American-cichlid guidance.
• Temperature: Stable within 28–31°C.
• Water chemistry: pH 4.8–6.2 and general hardness 1–5 dGH.
• Flow: Slow enough for the fish to hold position comfortably.

A clear aquarium can still contain ammonia or nitrite, so use test results rather than clarity as the decision. If either toxic compound is detectable, pause the introduction and restore biological stability. Keep the mature filter running continuously and avoid changes that remove or overwhelm its bacterial population.

Establish feeding with live food and a measured routine

Begin with suitable live foods and be prepared to offer them regularly while confirming that the fish is feeding. Seriously Fish describes feeding Altums as potentially troublesome and recommends live food, followed by a gradual transition to frozen food by mixing frozen and live items at the same meal. Once the fish accepts food reliably, a quality dried product can add variety; flake may also be accepted by aquarium-raised Altums.

Feed only what the fish can consume within a few minutes, once a day. That amount and schedule come from OATA’s American-cichlid guidance. Watch the individual take food instead of relying on food disappearing somewhere in a planted aquarium. Long fins, tall wood and group dynamics can make it difficult to see which fish actually ate.

Use feeding response to choose the next step

• If live food is taken promptly: Continue a modest portion and begin mixing in a small amount of frozen food.
• If frozen food is accepted: Increase variety gradually while retaining foods that produce a consistent feeding response.
• If dried food is accepted: Use a quality product as part of the rotation, while continuing to watch body condition and response.
• If food is repeatedly ignored: Test water quality, check temperature and look for intimidation or competition before offering more.
• If leftovers remain after a few minutes: Remove them and reduce the next portion.

Do not compensate for a missed meal by adding repeated large portions. OATA warns that overfeeding can lead to excess faeces or uneaten food that breaks down and releases toxic waste. Uneaten food also adds to the waste the filter has to process.

When several fish share the aquarium, place food where each animal can reach it without entering another fish’s immediate space. Observe the full group until every individual has taken food. A fish that hangs back while companions feed needs a check of social pressure, flow and food placement rather than a larger aquarium-wide ration.

Follow the arrival and acclimatisation sequence

Arrange for someone to receive the parcel because live fish must not be left unattended. Tropical Fish Co hand-bags fish in pure oxygen, uses an insulated poly box and adds a heat pack when the weather calls for it. The parcel is carried by a service licensed to transport live animals, with tracking and the confirmed arrival details sent by email.

Follow our delivery and Live Arrival Guarantee policy in this order.

Complete the policy steps in order

1. Film before opening: Start a short continuous unboxing video while the parcel is still sealed, then record it being opened and the fish still inside the bag.
2. Receive and inspect: Open and inspect the parcel on the day it arrives, keeping the video running in one continuous take.
3. Acclimatise: Float the bag for 20–30 minutes before releasing the fish.
4. Keep transport water separate: Never pour the bag water into the aquarium.

Check the prepared aquarium before the fish arrives. Confirm zero ammonia and zero nitrite, maintain 28–31°C, pH 4.8–6.2 and 1–5 dGH, and complete the layout and compatibility assessment before the fish enters the community.

After release, watch the fish’s swimming, breathing, colour, temperament and feeding closely. Increase the aquarium’s livestock load slowly so the mature filter can respond to the extra waste and food. Give the new fish a clear opportunity to feed, especially where established companions move rapidly at mealtimes.

The first practical checkpoint is simple: the fish should be able to hold position in the slow flow, move through the layout without obstruction and access food without persistent exclusion. If one of those conditions fails, correct that specific environmental or social factor rather than changing several parts of the aquarium at once.

Maintain water quality with a repeatable weekly routine

Change 25% of the water at least once every week and test ammonia and nitrite at least weekly. Siphon solid waste from the substrate during the partial change, and treat replacement tap water with conditioner to remove chlorine or chloramine before it enters the aquarium.

Prepare replacement water so the aquarium remains at 28–31°C, pH 4.8–6.2 and 1–5 dGH. Check the result after maintenance, particularly when the source water varies. A repeatable preparation method protects this soft, acidic set-up from drifting outside the narrow routine range.

Complete the maintenance in a fixed order

1. Test ammonia, nitrite and nitrate before disturbing the aquarium.
2. Remove 25% of the water while siphoning visible solid waste from the substrate.
3. Treat replacement tap water for chlorine and chloramine.
4. Match the replacement water to the established temperature, pH and hardness plan.
5. Check the filter for blocked inlets, outlets or reduced flow.
6. Return the aquarium to slow, effective circulation and retest when a reading or fish response causes concern.

If filter media needs cleaning, rinse it lightly in aquarium water removed during the partial change. Do not rinse it under the tap, because chlorine or chloramine may kill the beneficial bacteria established in the media. Clean only as needed to restore function rather than stripping every filter component at once.

Track results from week to week. A rising nitrate trend, recurring debris behind wood or falling filter flow calls for a specific adjustment to waste removal, feeding or filter maintenance. Ammonia and nitrite must remain zero; any detectable reading takes priority over cosmetic work in the aquarium.

Act on changes in behaviour, breathing or feeding

Check the fish during feeding and again while it moves normally through the aquarium. OATA identifies changes in swimming, colour, temperament, breathing, appearance, body condition and food intake as useful early warnings. Learn the individual’s normal posture and pace so a change is noticeable before it becomes severe.

Seriously Fish describes Altums as very weak to nitrate build-up and extremely prone to stress-related diseases. Keep nitrate within OATA’s limit of no more than 20 mg per litre above the normal tap-water level, while maintaining zero ammonia and zero nitrite. Correct a measurable water problem promptly and preserve the biological filter while doing so.

A short written log helps separate a one-off observation from a developing pattern. Note the water readings, feeding response, breathing rate and which companions were nearby. This makes the next action more precise and prevents repeated changes that obscure the original cause.

Screen every companion for size, water and feeding behaviour

Choose peaceful larger fish that share 28–31°C, pH 4.8–6.2 and 1–5 dGH. Seriously Fish warns that anything able to fit inside an Altum’s mouth is potential prey and specifically includes Neon Tetras, Guppies and Pygmy Rasboras. Avoid those examples and any other fish whose adult body size leaves it vulnerable to being swallowed.

Discus are a named possibility because Seriously Fish says Altums can live with them and notes similar water requirements. OATA names angelfish among the calmer American cichlids that can be mixed in a robust community aquarium with larger shoaling species. Neither description makes every Discus, shoaling species or individual aquarium an automatic match; adult size, aquarium capacity, water chemistry and feeding access still have to align.

Apply four checks to every proposed companion

• Mouth-size check: Exclude fish small enough to be swallowed now or after the Altum reaches 18 cm.
• Water check: Keep only animals suited to the same warm, very soft and acidic range.
• Temperament check: Choose peaceful animals that do not chase, crowd or damage long fins.
• Feeding check: Make sure every Altum can take its once-daily portion before faster fish consume it.

Watch individual behaviour after any introduction. Persistent chasing, damaged fins, hiding, missed meals or confinement to one part of the aquarium means the combination is failing, even if the species names appeared reasonable on paper. Separate the animals or revise the stocking plan before body condition declines.

Check every other companion against the same four points. For a planned mix, check every companion against the aquarium’s volume and height, the measured water values, each animal’s adult size and the number of each fish. Base the stocking on the actual aquarium rather than on a general tank-mate label.

Plan a pair or group without forcing social contact

Keep angelfish as a pair at minimum or in a suitably planned group. OATA describes angelfish as social and warns that solitary fish may become stressed. It also advises allowing 40 litres per adult angelfish when planning stocking, while its larger-cichlid threshold sets at least 300 litres for fish over 15 cm.

Apply both figures to the finished adult community. A pair calculated at 80 litres still falls under the at-least-300-litre threshold used for a species reaching 18 cm. For a group, start from 300 litres for the first pair and add 40 litres for every further adult before allowing space for other animals. Larger populations or additional fish increase the required capacity beyond that baseline.

Watch how the group uses its space

• At feeding: Every fish should reach food without repeated displacement.
• At rest: No individual should remain confined behind wood or in one corner.
• During interaction: Brief movement between areas must not become persistent chasing or fin damage.
• Across the aquarium: Cover and wood should create separation without trapping a weaker fish in a dead end.

Seriously Fish discusses growing six young Altums when the keeper’s specific aim is to find a breeding pair. That is a breeding-planning example rather than a compulsory household group size. Use the OATA pair-or-group instruction for routine social planning, then let aquarium capacity, adult size and observed behaviour determine how large the group can responsibly be.

If one animal stops feeding, hides more than normal or loses condition, test the water and assess social access immediately. Do not respond by adding more fish automatically. First confirm that the existing aquarium has sufficient capacity, height, cover and feeding opportunities for the animals already present.

Answer common questions before choosing this Altum

How big does the Inirida F1 Altum Angelfish get?

It reaches a recorded maximum total length of 18 cm. Plan the permanent aquarium around that adult figure rather than the selected dispatch size.

What size aquarium does Pterophyllum altum need?

Plan at least 300 litres and choose a tall aquarium that accommodates its extended fins. The volume is OATA’s broad American-cichlid guidance for fish over 15 cm, applied to an Altum that reaches 18 cm.

How many Inirida F1 Altum Angelfish should I keep together?

OATA’s angelfish guidance says to keep a pair at minimum or a group because solitary angelfish may become stressed; allow 40 litres per adult while retaining the at-least-300-litre larger-cichlid threshold.

Is Pterophyllum altum suitable for beginners?

We rate it advanced because it needs the FishBase and Seriously Fish overlap of 28–31°C, pH 4.8–6.2 and 1–5 dGH, plus a mature filter, slow flow and close attention to feeding and nitrate.

What does this Altum Angelfish eat?

Start with suitable live food, then mix in frozen food as it settles and accepts meals; a quality dried product can add variety. Feed only what it consumes within a few minutes, once a day.

What temperature and pH does Pterophyllum altum need?

Keep it at 28–31°C, pH 4.8–6.2 and 1–5 dGH. These routine values are the overlap of the FishBase environmental range and the Seriously Fish aquarium range.

Is this fish aggressive or likely to nip fins?

It will treat any fish small enough to fit in its mouth as food, including Neon Tetras, Guppies and Pygmy Rasboras, but it is fine with other peaceful, larger fish. Choose peaceful larger companions and act if chasing, fin damage, hiding or exclusion from food develops.

Which animals can this Altum Angelfish live with?

Seriously Fish names peaceful larger fish and Discus, while OATA names larger shoaling fish for calmer angelfish communities. Each companion must share the FishBase and Seriously Fish overlap of 28–31°C, pH 4.8–6.2 and 1–5 dGH and be too large to swallow.

How does this fish arrive alive in the UK?

Start a short continuous unboxing video while the parcel is still sealed, showing it being opened and the fish still in the bag, and make sure someone is present to receive it. Tropical Fish Co hand-bags it in pure oxygen, packs it in an insulated poly box with a heat pack when weather calls for one, and uses a licensed live-animal service. Float the bag for 20–30 minutes before release and never pour bag water into the aquarium.

References for identity and care planning

• FishBase: accepted scientific identity, family, native distribution, environmental range, maximum length and height.
• Seriously Fish: aquarium water range, layout, flow, feeding, behaviour, sexing and compatibility.
• OATA: American-cichlid aquarium capacity, social planning, feeding, maintenance and health monitoring.
• RSPCA: biological filtration and the aquarium nitrogen cycle.
• Tropical Fish Co delivery policy: packing, reception and acclimatisation.