Kuhli loach and Swordtail
Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.
Workable only in unusual circumstances. Not a pairing to plan around.
- Minimum volume
- 175 L
- Minimum length
- 115 cm
- Factors considered
- 7
Concerns
The shared band 24–26 °C sits at the top of one animal's range, so that animal is permanently at its limit even though the overlap looks generous. The overlap sits at the extreme of at least one animal's range, so that animal is permanently at its limit. A non-empty overlap is not the same as a suitable one.
Derived from: environment.temperature range position on both records
pH ranges overlap only across 7–7.5, which is tighter than most tap-water supplies hold naturally.
Derived from: environment.ph overlap width
Hardness overlap is narrow at 10–10 °dGH. Check your source water before committing to the pairing.
Derived from: environment.generalHardness overlap width
Why it can work
- Kuhli loach 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.
- Swordtail needs a group of at least 4. 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.
- Kuhli loach is active mainly after dark, so the two overlap less than the stocking list suggests. Feed the nocturnal animal after lights-out or it will be outcompeted.
Conditions
Most interesting pairings are conditional on something. These are the things the keeper can actually change.
- At least 6 Kuhli loach, counted as one group
- At least 4 Swordtail, counted as one group
- At least 175 L with a footprint of 115 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
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.
| Dimension | Assessment | What that means here |
|---|---|---|
| Temperature | One animal at the edge of its range | The shared band 24–26 °C sits at the top of one animal's range, so that animal is permanently at its limit even though the overlap looks generous. |
| pH | Forced compromise — neither animal is where it wants to be | The shared band 7–7.5 pH sits at the top of one animal's range and the bottom 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 10–10 °dGH sits at the top of one animal's range and the bottom 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.
| Factor | Basis | Finding |
|---|---|---|
| Temperature | Derived from stored traits | One animal at the edge of its range. The shared band 24–26 °C sits at the top of one animal's range, so that animal is permanently at its limit even though the overlap looks generous. |
| 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 top of one animal's range and the bottom of the other's. Both would be kept at their limits to accommodate the other. |
| Hardness | Derived from stored traits | Forced compromise — neither animal is where it wants to be. The shared band 10–10 °dGH sits at the top of one animal's range and the bottom of the other's. Both would be kept at their limits to accommodate the other. |
| Body size | Derived from stored traits | Adult sizes are comparable at about 10 cm and 14 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 "moderate". It bears on the pairing because a fish under pressure from its own kind redirects. |
| Social requirements | Derived from stored traits | Kuhli loach needs at least 6; Swordtail needs at least 4. 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 "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 150 L and 100 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 | 24–26 °C | Aim for the middle of the shared band. |
| pH | 7–7.5 | Stability matters more than the exact figure. |
| Hardness | 10–10 °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 Kuhli loach or Swordtail.
- 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.