Freshwater fish compatibility checker

How the checker works

The checker compares every pair of species you select, using the same data you see on each profile. For each pair it looks at several factors and returns a verdict: good, caution or not compatible. The overall result for the tank is the worst verdict among all pairs.

What it compares

• Water ranges: temperature, pH and hardness must overlap. Small overlaps produce a caution; no overlap means they should not share a tank.
• Size and predation: if one species is large enough to swallow the other, it is flagged. Predatory species get a stricter check.
• Temperament: aggressive and semi-aggressive fish are compared with peaceful ones, considering size and territory.
• Fin nipping: known nippers are flagged with long-finned or slow species such as bettas, angelfish and fancy guppies.
• Shrimp and snail safety: fish that eat invertebrates are flagged when you add shrimp or snails.

How to read the results

A good verdict means our data show no relevant conflict. A caution means it can work under certain conditions, for example a larger tank, more cover, the right group size or water in the middle of both ranges. Read the reason listed and decide if you can meet it. Not compatible means a clear conflict, such as predation or incompatible water.

The checker does not know your tank size or the personality of each fish. Individuals vary: a betta may ignore shrimp or hunt them. Combine the result with the stocking calculator to make sure everything fits in your volume.

Tips for a successful mix

Choose species with similar water needs, add fish gradually to a cycled tank, respect minimum group sizes, and provide plants and hiding places. When in doubt, choose fewer species in larger groups.