Fish for hard, alkaline water
16 species from the AquaLog care guide · Updated
In short: If your tap water is hard and alkaline (pH 7 or higher), keep fish that want it: livebearers such as guppies, platies and mollies, many rainbowfish, and African rift lake cichlids. Working with your water is far easier than softening it.
Hard water carries a lot of dissolved calcium and magnesium (high GH) and usually a high pH. Borewell and well water often run hard. Every species below has a minimum pH of 7 or higher in the AquaLog care guide: these fish do best in exactly the water many people already have.
Test your tap water's pH, GH and KH first. See aquarium water parameters explained.
The species
| Species | Min. tank | Temperature | pH | Temperament | Group | Care level |
|---|---|---|---|---|---|---|
| EndlerPoecilia wingei | 30 L (8 gal) | 22–29 °C | 7–8.5 | Peaceful | 3+ | Beginner |
| Dwarf emerald rasboraCelestichthys erythromicron | 40 L (11 gal) | 21–26 °C | 7–8 | Peaceful | 8+ | Intermediate |
| GuppyPoecilia reticulata | 40 L (11 gal) | 22–28 °C | 7–8.5 | Peaceful | 3+ | Beginner |
| PlatyXiphophorus maculatus | 60 L (16 gal) | 20–27 °C | 7–8.5 | Peaceful | 3+ | Beginner |
| MultiesNeolamprologus multifasciatus | 75 L (20 gal) | 24–27 °C | 7.8–9 | Semi-aggressive | 6+ | Intermediate |
| MollyPoecilia sphenops | 90 L (24 gal) | 24–28 °C | 7.5–8.5 | Peaceful | 3+ | Beginner |
| Celebes rainbowfishMarosatherina ladigesi | 110 L (29 gal) | 24–29 °C | 7–8.5 | Peaceful | 6+ | Intermediate |
| SwordtailXiphophorus hellerii | 110 L (29 gal) | 22–28 °C | 7–8.4 | Semi-aggressive | 3+ | Beginner |
| Fancy goldfishCarassius auratus | 150 L (40 gal) | 16–23 °C | 7–8.4 | Peaceful | 2+ | Intermediate |
| Turquoise rainbowfishMelanotaenia lacustris | 190 L (50 gal) | 22–28 °C | 7–8.5 | Peaceful | 6+ | Intermediate |
| Boesemani rainbowfishMelanotaenia boesemani | 200 L (53 gal) | 24–30 °C | 7–8.5 | Peaceful | 6+ | Beginner |
| Yellow lab cichlidLabidochromis caeruleus | 200 L (53 gal) | 24–28 °C | 7.6–8.8 | Semi-aggressive | 4+ | Intermediate |
| Zebra mbunaMaylandia zebra | 250 L (66 gal) | 24–28 °C | 7.6–8.8 | Aggressive | 4+ | Advanced |
| Peacock cichlidAulonocara stuartgranti | 300 L (79 gal) | 24–28 °C | 7.6–8.6 | Semi-aggressive | 4+ | Intermediate |
| FrontosaCyphotilapia frontosa | 570 L (151 gal) | 24–27 °C | 7.8–9 | Semi-aggressive | 5+ | Advanced |
| KoiCyprinus rubrofuscus | 3800 L (1004 gal) | 4–28 °C | 7–8.5 | Peaceful | 4+ | Intermediate |
African cichlids need more than hard water
The rift lake cichlids here are territorial and most need large tanks. Check each species' minimum tank size and temperament before buying; several are rated semi-aggressive or aggressive.
A note on koi and goldfish
Fancy goldfish are cold-water fish and shouldn't share a tropical tank. Koi belong in ponds; the care guide's minimum is thousands of litres.
Snails like hard water too
Nerite and mystery snails also prefer pH 7 or higher; the minerals in hard water help keep their shells strong.