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Tap water match: which fish suit your water?

Enter your tap's pH and hardness — see which of our 222 species would thrive in it untreated.

Temperature isn't asked for — your heater decides that. This matches the chemistry you can't easily change: pH and hardness.

Create a free account to save these numbers once — after that every plan and every tank is scored against your water.

140 species find this water ideal · 129 more tolerate it.

Fish 173

Thrive untreated — inside their optimal band

Tolerate it — inside their comfortable range

Invertebrates 19

Thrive untreated — inside their optimal band

Tolerate it — inside their comfortable range

Plants 77

Thrive untreated — inside their optimal band

Tolerate it — inside their comfortable range

Plan a tank with this water →

The easiest tank to keep is the one your tap water already suits, because every alternative costs money and attention forever. Softening, remineralising and pH adjustment all work, and all of them add a step you now have to get right every week for years — and the week you get it wrong is the week the parameters swing, which is harder on fish than the wrong stable value ever was. With hundreds of species spanning almost every freshwater chemistry on earth, starting from your own supply is nearly always the better trade. Two cautions on the numbers you feed in. Your water company's published pH is measured at the treatment plant, not your kitchen, and it moves in transit: water leaves under pressure carrying dissolved CO₂, and once it sits in an open bucket that CO₂ gasses off and the pH climbs — often by half a point or more. Test a glass that has stood overnight, not one straight from the tap, or you will plan around a number your tank never sees. And do not confuse the two hardnesses: GH is calcium and magnesium, which is what most species' ranges refer to, while KH is carbonates and is what stops your pH moving. A soft-water fish minds GH; a stable pH depends on KH.

Common questions

How do I find out my tap water's pH, GH and KH?
A basic test strip covers all three in seconds, liquid test kits are more precise, and most water utilities publish hardness in their annual quality report — though utility figures may be in mg/L CaCO₃ (divide by 17.86 to get °dGH) and won't include the pH after it has off-gassed overnight, which is the number your tank actually sees.
Can I keep soft-water fish in hard tap water?
Many tolerate it, but tolerating isn't thriving: hard, alkaline water shortens the comfortable margin for blackwater species and can stop some from breeding. If your tap is hard, the happier route is usually hard-water species — livebearers, rainbowfish, Rift Lake cichlids — rather than fighting your chemistry every water change.
My tap pH reads differently after sitting overnight — which one is right?
The one that stood overnight. Mains water is pressurised and carries more dissolved CO₂ than it will hold at atmospheric pressure; as that gasses off the pH rises, often by 0.3–0.7. Your tank sees the settled value, so that is the number to plan with — and it is also why a bucket left standing before a water change is a small, free improvement.

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