Conditional1 concerns

Guppy and Neon tetra

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

VerdictConditionalhigh confidence

Can work, but only if the stated conditions are met.

Minimum volume: 60 L
Minimum length: 60 cm
Factors considered: 6

Concerns

moderateph

pH ranges overlap only across 7–7.5, which is tighter than most tap-water supplies hold naturally.

Derived from: environment.ph overlap width

Why it can work

Temperature requirements overlap comfortably at 22–26 °C, with room for both animals to sit inside their preferred range.
Hardness requirements overlap at 8–10 °dGH.
Guppy 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.
Neon tetra needs a group of at least 8. 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.
The two occupy different levels of the tank, which reduces direct competition for space.

Conditions

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

At least 6 Guppy, counted as one group
At least 8 Neon tetra, counted as one group
At least 60 L with a footprint of 60 cm or more, before counting anything else in the tank

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

Widely reported in practice

Reported consistently across aquarium practice without a single citable source. Treated as real but not as measurement.

AquariumHQ's overall position

Behaviourally unremarkable and chemically a genuine compromise. Kept in the middle both persist and neither is where it wants to be, which shows up as shortened lifespan rather than as visible trouble.

Factor by factor

Hardness pulls in opposite directionsReported
Guppies are hard-water livebearers and neon tetras are soft-water characins. This is the substantive incompatibility and it is invisible in a shop, because both survive the middle ground long enough to be sold together.
TemperatureDerived
Both tolerate the middle of the community range, so temperature is the easier of the two water questions.
BehaviourReported
No aggression or predation between them at adult sizes. The pairing fails, where it fails, on water chemistry rather than on behaviour.

What the answer depends on. A single cell in a compatibility chart cannot hold any of these.
Depends on	How much
Tank size and dimensions	none
Life stage	none
The individual animal	minor

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	Comfortable for both	The shared band 22–26 °C sits centrally in both ranges, with room to drift.
pH	Forced compromise — neither animal is where it wants to be	The shared band 7–7.5 pH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other.
Hardness	Forced compromise — neither animal is where it wants to be	The shared band 8–10 °dGH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other.

Forced compromise — neither animal is where it wants to be

Both animals would be kept at the edge of their ranges to accommodate the other. Nothing here is a recommendation; it is the arithmetic of two incompatible requirements meeting at a point.

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.

3 evidence-backed16 derived0 not known

Factor	Basis	Finding
Temperature	Derived from stored traits	Comfortable for both. The shared band 22–26 °C sits centrally in both ranges, with room to drift.
pH	Derived from stored traits	Forced compromise — neither animal is where it wants to be. The shared band 7–7.5 pH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other.
Hardness	Evidence-backed	Forced compromise — neither animal is where it wants to be. The shared band 8–10 °dGH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other. Reported: Guppies are hard-water livebearers and neon tetras are soft-water characins. This is the substantive incompatibility and it is invisible in a shop, because both survive the middle ground long enough to be sold together.
Body size	Derived from stored traits	Adult sizes are comparable at about 6 cm and 3.5 cm, so neither is a mouthful for the other.
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 "none". It bears on the pairing because a fish under pressure from its own kind redirects.
Social requirements	Derived from stored traits	Guppy needs at least 6; Neon tetra needs at least 8. 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	The two use different levels of the tank, which reduces direct competition for space.
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 "moderate".
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 60 L and 60 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	Evidence-backed	Life-stage dependency: none. See the documented record.
Individual variation	Evidence-backed	Individual variation: minor.

Environmental overlap

Parameter	Shared range	Reading
Temperature	22–26 °C	Aim for the middle of the shared band.
pH	7–7.5	Stability matters more than the exact figure.
Hardness	8–10 °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 Guppy or Neon 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

GuppyPoecilia reticulataDomestic guppies are hard-water fish, which is the opposite of what most people assume. They are also among the most widely introduced fish on Earth — released deliberately for mosquito control and now established across the tropics with documented harm to native species.Neon tetraParacheirodon innesiThe best-known aquarium fish in the world, and one of the most frequently misjudged. Neons are commercially bred in enormous numbers, which has made them cheap but not hardy — farmed stock is notably less robust than the species' reputation suggests, and losses in the first weeks after purchase are common.