Generally compatible2 concerns

Black ruby barb and Ember tetra

Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.

VerdictGenerally compatiblemoderate confidence

Usually works. Minor points to watch are listed below.

Minimum volume: 125 L
Minimum length: 105 cm
Factors considered: 6

Concerns

minortemperature

Temperature requirements overlap at 23–26 °C, though the band does not sit centrally for both animals. Aim for the middle of it and keep the heater accurate.

Derived from: environment.temperature on both records

minorzone competition

Both species occupy the midwater of the tank, so allow for the shared space when judging the footprint.

Derived from: zone and traits.activity on both records

Why it can work

pH requirements overlap at 6–7.
Hardness requirements overlap at 2–8 °dGH.
Black ruby barb needs a group of at least 6. Kept in smaller numbers it is not simply lonely — shoaling species held below their threshold show chronic stress behaviour, colour loss and, in several species, increased aggression towards tankmates.
Ember tetra needs a group of at least 10. Kept in smaller numbers it is not simply lonely — shoaling species held below their threshold show chronic stress behaviour, colour loss and, in several species, increased aggression towards tankmates.

Conditions

Most interesting pairings are conditional on something. These are the things the keeper can actually change.

At least 6 Black ruby barb, counted as one group
At least 10 Ember tetra, counted as one group

Derived, or documented?

These are different claims and are shown separately. The verdict above is derived from stored traits — arithmetic on AquariumHQ's own records. Whether the pairing is actually reported to work is a separate question, and for most pairs the honest answer is that we hold nothing.

Environmental compatibility

Derived from stored traits

Temperature, pH, hardness, size and behavioural traits compared between the two records. Sound as far as it goes, and it is not evidence that the pairing works.

Behavioural evidence

No behavioural evidence held

AquariumHQ holds no behavioural evidence for this pairing. The verdict is derived entirely from stored traits — it is arithmetic on our own records, not a report about how the pairing actually goes.

How good is the overlap?

Whether two ranges intersect is a necessary condition, not evidence. What matters is WHERE the shared band sits: an overlap at the top of one animal's range and the bottom of the other's is a forced compromise however wide it looks, and it is the case a simple intersection test cannot see.

Each dimension assessed for the quality of the overlap, not merely its existence.
Dimension	Assessment	What that means here
Temperature	Workable	The shared band 23–26 °C is usable, though it does not sit centrally for both animals.
pH	Workable	The shared band 6–7 pH is usable, though it does not sit centrally for both animals.
Hardness	Workable	The shared band 2–8 °dGH is usable, though it does not sit centrally for both animals.

Factor by factor

Every factor states what it rests on. Most are derived from the traits stored on both records — sound arithmetic on AquariumHQ's own data, and not a report about how the pairing actually goes. Where a factor says 'not known', the data is missing and saying so matters, because a missing factor and a favourable one look identical once both are absent.

0 evidence-backed17 derived2 not known

Factor	Basis	Finding
Temperature	Derived from stored traits	Workable. The shared band 23–26 °C is usable, though it does not sit centrally for both animals.
pH	Derived from stored traits	Workable. The shared band 6–7 pH is usable, though it does not sit centrally for both animals.
Hardness	Derived from stored traits	Workable. The shared band 2–8 °dGH is usable, though it does not sit centrally for both animals.
Body size	Derived from stored traits	Black ruby barb reaches about 6.5 cm against 2.2 cm for Ember tetra — a ratio of 3.0. Size disparity drives opportunistic predation independently of temperament.
Predation	Derived from stored traits	Highest predation risk in either direction is "none".
Territoriality	Derived from stored traits	Neither animal holds a territory.
Breeding aggression	Derived from stored traits	Neither becomes notably more aggressive while spawning.
Fin-nipping	Derived from stored traits	No nipper-and-target combination between these two.
Aggression	Derived from stored traits	Strongest intraspecific aggression across the pair is "mild". It bears on the pairing because a fish under pressure from its own kind redirects.
Social requirements	Derived from stored traits	Black ruby barb needs at least 6; Ember tetra needs at least 10. A shoaling species held below its threshold shows chronic stress and, in several species, increased aggression towards tankmates.
Group-size dependency	Derived from stored traits	The outcome depends on group size as much as on the pairing: under-grouped shoalers nip more and hide more.
Tank zone	Derived from stored traits	Both occupy the midwater of the tank, so the shared space is under pressure.
Activity level	Derived from stored traits	Activity levels are compatible.
Food competition	Derived from stored traits	Different feeding strategies, so direct competition is limited.
Risk to shrimp and snails	Derived from stored traits	Highest risk either animal poses to dwarf shrimp or snails is "high".
Effect on plants	Derived from stored traits	Neither animal damages planting.
Tank dimensions	Derived from stored traits	The more demanding of the two needs at least 90 L and 75 cm of length before anything else is in the tank. Volume alone does not describe a home for a fish that swims in straight lines.
Life stage	Not known	AquariumHQ holds no record of whether this pairing changes as either animal matures. Stored traits describe adults, so a pairing that fails at adult size looks identical to one that never fails.
Individual variation	Not known	AquariumHQ holds no record of how much this pairing varies between individuals. For several species — bettas and cichlids especially — that variation decides the outcome and a species-level verdict cannot express it.

Environmental overlap

Parameter	Shared range	Reading
Temperature	23–26 °C	Aim for the middle of the shared band.
pH	6–7	Stability matters more than the exact figure.
Hardness	2–8 °dGH	Check your source water before committing.

What this assessment cannot tell you

Individual temperament varies, particularly in cichlids and in bettas, and can override a favourable verdict for Black ruby barb or Ember tetra.
The assessment is for the pair in isolation. A third species can change the outcome in either direction.
Both animals are assessed at adult size, not at the size they are sold.
A verdict is a statement about probability, not a guarantee.

The two species

Black ruby barbPethia nigrofasciataA Sri Lankan endemic whose males turn deep crimson-black when displaying, and one of the few barbs whose colour is a behaviour rather than a fixed pattern. Populations in the wild have declined substantially through collection and habitat loss; trade stock is almost entirely captive-bred.Ember tetraHyphessobrycon amandaeA two-centimetre orange characin that has become one of the most useful small community fish available — peaceful, adaptable within reason, and small enough to suit tanks where a neon shoal would be cramped.