Freshwater Fish · Tetras

Rummy-nose Tetra

Petitella rhodostoma

One of the tightest schoolers in the hobby, with a built-in stress gaugeIntermediate

Lifespan: 5-6 years
Size: 2 in
Social needs: Tight schooler; keep 10+ together
Time: 10-15 min daily; weekly water change
Cost: Low-Medium
Diet: Omnivore (micro-pellet, flake, frozen foods)

Overview

What is this animal?

Rummy-nose tetras are silver torpedoes with a glowing red face and a boldly striped tail, famous for schooling more tightly than almost any other aquarium fish.
A group moving as one is a genuine spectacle.
Long known as Hemigrammus rhodostomus, it was moved to the genus Petitella in 2020, and many fish sold as rummy-noses are in fact the near-identical firehead tetra, Petitella bleheri, which needs the same care.

They carry a built-in diagnostic: the red nose drains to washed-out pink when the fish are stressed or the water deteriorates, making the school a live water-quality gauge.

Temperament

Completely peaceful, rummy-noses spend the day cruising in formation through the lower midwater.
The tighter the school, the more secure the fish; small groups huddle and hide instead.

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They are ideal companions for other gentle blackwater species: cardinal tetras, corydoras, dwarf cichlids, and pencilfish.
Nothing about them threatens shrimp colonies beyond the odd newborn.

A good fit for

Keepers who want true, dramatic schooling behaviour
Mature planted aquariums with stable parameters
Communities with dwarf cichlids and corydoras
Aquarists who like visible feedback on water quality

Common mistakes to avoid

Adding them to brand-new, unstable tanks
Groups under 10 that huddle rather than school
Temperature and parameter swings: noses fade fast
Buying freshly imported, unrested stock

Enclosure

Minimum 30 gallons, for a group of 10

Cannot be kept alone. The minimum is 10, and the space above is for that group.

Keep a school of ten or more in a mature, cycled aquarium of at least 30 US gallons and 3 ft long, such as a standard 30-gallon (36 x 12 x 16 in); 35 in is the minimum length Seriously Fish gives, and bigger groups in longer tanks school more impressively.
Provide open swimming length with planted flanks.

Hold the temperature at 75-82°F.
They come from soft, acidic blackwater, and while tank-bred stock adapts to moderately hard water, what they cannot forgive is instability: drift and spikes show in the noses immediately.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Micro-pellet or finely crushed tropical flake
Frozen daphnia and cyclops
Frozen or live baby brine shrimp
Microworm culture (optional, for fry and conditioning)
Spirulina-based flake

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Fine net for removing leftovers
Small feeding spoon for accurate pinches

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

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Weekly

Count the school
Test the water
Water change and gravel vacuum
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly school and stability review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore (micro-pellet, flake, frozen foods)

Offer fine flake or micro-pellets as the staple, with regular frozen or live treats such as daphnia, cyclops, baby brine shrimp, and chopped bloodworm.
Their mouths are small, so size food accordingly.

Feed once or twice daily in small amounts.
A well-fed, settled school shows saturated red noses at every feed.

Health

Signs of good health, and the common problems

Rummy-noses are not delicate once settled, but they ship poorly and resent new, unstable tanks; add them to mature aquariums only and quarantine first.
Losses in the first fortnight usually mean the tank, not the fish, was not ready.

After that, standard tetra care applies: watch for ich after temperature dips and keep nitrate low with steady weekly water changes.
Faded noses are the early-warning sign: investigate before anything else goes wrong.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Tetras yet.

Top resources for more info

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