Compatibility
45%
Group needs, aggression, predation and species conflicts.
Methodology · version 2026.08
What the FishTankr score means
The score helps you spot problems in a stocking plan. It cannot prove a tank is safe. It uses checks we can explain clearly. Early estimates stay separate until the evidence is stronger.
Swimming space
35%
Adult size, minimum tank volume and swimming length.
Water suitability
20%
The selected pH and temperature against each species.
The cycle can limit the score
A fast pump does not automatically mean strong biological filtration. We check the filter, biological media, tank age, cycling method and recent water tests. If the cycle is unfinished or unverified, the score is limited. If ammonia or nitrite is present, do not add fish.
We ask for zero-ammonia and zero-nitrite results from the past seven days. That keeps the plan tied to reasonably recent information; it does not mean one test can predict what happens next. No single reading or fixed number of weeks proves that a tank is ready.
One big problem outweighs a good average
Great water can't make up for a fish that gets eaten. Any critical problem, like predation or a tank that's far too small, caps the score at 40. Any serious problem caps it at 70, so the plan can't show as looking good until it's fixed.
Current beta limitation
The waste-load screen is not a stocking-capacity calculator
This estimate uses an older species-load formula that has not been tested against enough real aquariums. It only shows a broad band. It does not affect the main score. Extra flow, plants or maintenance cannot make the number look better. It never tells you how many more fish to add.
It will stay in beta until we have a sourced model for fish waste and biological filtration, tested against independently reviewed tank examples.
Evidence policy
What counts
- Care information linked to a named source and review date
- Clear confidence labels when sources are incomplete or disagree
- Safety rules we can explain in plain language
- Test tanks reviewed independently from the code
What FishTankr does not claim
- A universal number of fish per litre
- That a faster pump means better biological filtration
- That plants or water changes can make incompatible fish safe together
- That a score can replace watching the fish, testing the water or getting expert help
Research behind the approach
These studies support looking at biofilter maturity, water quality and several parts of fish welfare separately. They do not prove that the beta waste-load estimate is accurate.