Goldfish and Kuhli loach
Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.
Should not be attempted. At least one factor is expected to cause harm.
- Minimum volume
- 460 L
- Minimum length
- 165 cm
- Factors considered
- 7
Concerns
Temperature requirements do not overlap: 10–22 °C for Goldfish against 24–29 °C for Kuhli loach. One animal would be kept outside its range permanently.
Derived from: environment.temperature on both records
Goldfish reaches about 35 cm and takes fish small enough to swallow. At roughly 10 cm, an adult Kuhli loach is inside that range. This is usually discovered as fish quietly disappearing overnight rather than as visible aggression. Goldfish has a small terminal mouth and Kuhli loach is eel-like, so the size at which Kuhli loach stops being a possible mouthful is HIGHER than the usual third-of-body-length rule — around 78% of Goldfish's length rather than 40%.
Derived from: traits.predation.smallFish, adultSize on both records, and the stored body form and gape of both
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
- Hardness requirements overlap at 8–10 °dGH.
- 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.
- 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
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 | No overlap at all | Ranges do not meet: 10–22 against 24–29 °C. |
| 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. |
No overlap at all
The ranges do not meet. One animal would be kept outside its range permanently.
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 | No overlap at all. Ranges do not meet: 10–22 against 24–29 °C. |
| 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 | Derived from stored traits | 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. |
| Body size | Derived from stored traits | Goldfish reaches about 35 cm against 10 cm for Kuhli loach — a ratio of 3.5. Size disparity drives opportunistic predation independently of temperament. |
| Predation | Derived from stored traits | Highest predation risk in either direction is "moderate". |
| 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 | Kuhli loach needs at least 6. 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 "near-certain". |
| Effect on plants | Derived from stored traits | Goldfish eats plants, which constrains the aquascape rather than the pairing. |
| Tank dimensions | Derived from stored traits | The more demanding of the two needs at least 400 L and 150 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 | No overlap | One animal would be kept outside its range. |
| 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 Goldfish or Kuhli loach.
- 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.
Where the two water bands meet
Derived from the ranges AquariumHQ publishes for each species. The compatibility engine reads the same numbers; this is what they look like drawn on one axis.
Temperature (°C)
Scale: 0 to 36 °C.
No overlap. There is no temperature at which both species are inside their advised range.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Why the bands sit where they do
The overlap above is arithmetic. This is where the two numbers came from — the kind of water each animal is recorded from, and how much room that leaves.
These two animals come from different kinds of water, and that is where the arithmetic below comes from rather than from anything about their temperaments.
Goldfish
No wild referent
variable flow · not characteristic oxygen
Kuhli loach
Soft forest stream
20–120 µS/cm · low flow · moderate oxygen
- TemperatureGoldfish 10–22°CKuhli loach 24–29°C
No overlap.
No overlap at all. There is no temperature, pH or hardness that suits both.
- pHGoldfish 7–8.5Kuhli loach 5–7.5
Both inside their range from 7–7.5 — 33% of the narrower animal’s range.
A real window, and a narrow one. The tank has to be held inside it, and there is little room for the drift that happens between water changes.
- General hardnessGoldfish 8–25 dGHKuhli loach 1–10 dGH
Both inside their range from 8–10 dGH — 22% of the narrower animal’s range.
Barely an overlap. Whatever is chosen, at least one animal spends its life at the limit of its published range — which is survivable and is not the same as suitable.
Computed from the ranges AquariumHQ publishes for each species, each of which records what it rests on — a source value, a habitat inference, a physiological requirement or a trade convention. Most are habitat inferences, and the species pages say which.