Aquarium fish compatibility checker
Planning a new addition? Check how its needs fit your tank and the species you already keep.
Some stocking problems are visible before anything goes in the water: mismatched temperature ranges, a shoaling species kept alone, or a peaceful community paired with a territorial adult. The OneShoal.com compatibility checker takes species from your saved listings, with an optional tank you already keep, and explains each result in plain English so you can adjust the plan rather than rehome a fish later.
Free with a OneShoal.com account. Guidance only — it never replaces your own judgement.
What the checker looks at
Water type and parameters
Freshwater, brackish or marine, plus overlapping temperature and pH ranges so nothing is kept outside what it tolerates.
Tank size and stocking load
Adult size and bioload against your tank volume, so a peaceful pairing does not quietly become an overstocked one.
Temperament and fin nipping
Known aggression, territorial behaviour and fin nipping risks flagged before you add anything to an established tank.
Shoaling and group minimums
Species that need a group are checked against the numbers you actually plan to keep, not a single specimen.
How it works
- 1Save the relevant marketplace listings first.
- 2Open the checker and select up to 12 saved species.
- 3Optionally choose a tank or pond from My Shoal to include the fish and readings you've saved.
- 4Read the results, including any risks or missing information, before changing your selection.
Common questions
- What fish can live together in one tank?
- Fish can share a tank when their water type, temperature and pH ranges overlap, their temperament is compatible, the tank is large enough for every adult size, and any shoaling species are kept in adequate groups. The OneShoal.com compatibility checker tests each of those in turn and explains every warning in plain English.
- Is the compatibility checker free to use?
- Yes. The checker is free for OneShoal.com members, in every country we operate in. You create a free account so your tanks and saved species stay with you between visits, and so results can be checked against the tanks you already keep.
- Can I check fish against a tank I already have?
- Yes. If you have added a tank in My Shoal, you can compare species from your saved listings with that tank's water type, volume and recorded stock.
- Does a green result guarantee the fish will get on?
- No. Compatibility guidance reduces obvious risk, but individual fish, aquascaping, feeding and the order you introduce stock all matter. Always quarantine new arrivals and watch behaviour closely for the first few weeks.
Ready to plan your stocking?
Open the checker, or review responsible fishkeeping guidance first.