Goldfish and Silver dollar
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
- 5
Concerns
Temperature requirements do not overlap: 10–22 °C for Goldfish against 24–28 °C for Silver dollar. One animal would be kept outside its range permanently.
Derived from: environment.temperature on both records
pH ranges overlap only across 7–7.2, which is tighter than most tap-water supplies hold naturally.
Derived from: environment.ph overlap width
Why it can work
- Hardness requirements overlap at 8–12 °dGH.
- Silver dollar 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.
- At least 5 Silver dollar, 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 24–28 °C. |
| pH | Forced compromise — neither animal is where it wants to be | The shared band 7–7.2 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 | One animal at the edge of its range | The shared band 8–12 °dGH sits at the bottom of one animal's range, so that animal is permanently at its limit even though the overlap looks generous. |
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 24–28 °C. |
| pH | Derived from stored traits | Forced compromise — neither animal is where it wants to be. The shared band 7–7.2 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 | One animal at the edge of its range. The shared band 8–12 °dGH sits at the bottom of one animal's range, so that animal is permanently at its limit even though the overlap looks generous. |
| Body size | Derived from stored traits | Goldfish reaches about 35 cm against 15 cm for Silver dollar — a ratio of 2.3. 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 | Silver dollar 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 | 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 | 7–7.2 | Stability matters more than the exact figure. |
| Hardness | 8–12 °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 Silver dollar.
- 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
Silver dollar
Clearwater lowland river
20–100 µS/cm · moderate flow · near saturation oxygen
- TemperatureGoldfish 10–22°CSilver dollar 24–28°C
No overlap.
No overlap at all. There is no temperature, pH or hardness that suits both.
- pHGoldfish 7–8.5Silver dollar 5.5–7.2
Both inside their range from 7–7.2 — 13% 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 hardnessGoldfish 8–25 dGHSilver dollar 2–12 dGH
Both inside their range from 8–12 dGH — 40% 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.