Rainbow shark and Red zebra cichlid
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
- 375 L
- Minimum length
- 165 cm
- Factors considered
- 7
Concerns
Both animals hold strong territories. Two strongly territorial residents in one tank means continuous boundary pressure unless the footprint is large enough to give each an independent area with sightline breaks.
Derived from: traits.territoriality on both records
pH ranges overlap only across 7.6–7.8, which is tighter than most tap-water supplies hold naturally.
Derived from: environment.ph overlap width
Red zebra cichlid becomes markedly more aggressive while spawning. A pairing that has been peaceful for months can change within a day, so plan for where the other animal goes if it does.
Derived from: traits.breedingAggression
Temperature requirements overlap at 24–27 °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
Why it can work
- Hardness requirements overlap at 10–15 °dGH.
- Red zebra cichlid needs a group of at least 5. 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.
- A long tank with hardscape dividing it into visually separate territories
- At least 5 Red zebra cichlid, counted as one group
- At least 375 L with a footprint of 165 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 | Workable | The shared band 24–27 °C is usable, though it does not sit centrally for both animals. |
| pH | Forced compromise — neither animal is where it wants to be | The shared band 7.6–7.8 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 | Workable | The shared band 10–15 °dGH is usable, though it does not sit centrally for both animals. |
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 | Workable. The shared band 24–27 °C is usable, though it does not sit centrally for both animals. |
| pH | Derived from stored traits | Forced compromise — neither animal is where it wants to be. The shared band 7.6–7.8 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 | Workable. The shared band 10–15 °dGH is usable, though it does not sit centrally for both animals. |
| Body size | Derived from stored traits | Adult sizes are comparable at about 15 cm and 13 cm, so neither is a mouthful for the other. |
| Predation | Derived from stored traits | Highest predation risk in either direction is "high". |
| Territoriality | Derived from stored traits | Strongest territoriality across the pair is "strong". |
| Breeding aggression | Derived from stored traits | Breeding aggression reaches "strong". A pairing peaceful for months can change within a day of a spawn. |
| 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 "strong". It bears on the pairing because a fish under pressure from its own kind redirects. |
| Social requirements | Derived from stored traits | Red zebra cichlid needs at least 5. 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 | Red zebra cichlid 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 250 L and 120 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 | 24–27 °C | Aim for the middle of the shared band. |
| pH | 7.6–7.8 | Stability matters more than the exact figure. |
| Hardness | 10–15 °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 Rainbow shark or Red zebra cichlid.
- 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.
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.
Rainbow shark
Lowland floodplain
40–300 µS/cm · still flow · low oxygen
Red zebra cichlid
Lake Malawi
200–280 µS/cm · low flow · near saturation oxygen
- TemperatureRainbow shark 22–27°CRed zebra cichlid 24–28°C
Both inside their range from 24–27°C — 75% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
- pHRainbow shark 6.5–7.8Red zebra cichlid 7.6–8.6
Both inside their range from 7.6–7.8 — 20% 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.
- General hardnessRainbow shark 5–15 dGHRed zebra cichlid 10–20 dGH
Both inside their range from 10–15 dGH — 50% 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.
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.