What can I keep in my hard water aquarium?


A reader asks what fish she can keep in her hard water aquarium...

Q) I live in a very hard water area and even using half ‘perfect water’ for my weekly water changes, I’m still only achieving pH8, GH10 and KH7. Which fish would be happy in those parameters, in my 90 l tank please?


A) Neale says: Many of the tropical fish we see in the shops prefer soft water, but there are plenty that don’t. While fish from South America, West Africa, and Southeast Asia certainly do, Central American species do not, and that includes all sorts of lovely livebearers and some more challenging cichlids. Likewise, the Rift Valley cichlids aren’t soft water fish by any means, though the nitrate levels in ‘London tap’ doesn’t do them any good. Rainbowfish are a mixed bag, with some species preferring or even requiring soft water, but most doing well in neutral, even moderately hard water conditions.

But the reality is that many of the species from fish farms have become less demanding in terms of water chemistry than their wild ancestors, and for a good many species, what we see in aquarium shops are somewhat more adaptable than you might think, particularly if maintenance, rather than breeding is the goal. Quite a few tetras, for example, will do perfectly well in moderately hard water (up to 20˚dH) including X-ray tetras, Emperor tetras, False penguin tetras, Black widow tetras and Serpae tetras, although the nippy behaviour of the latter makes them better suited to single-species set-ups rather than community tanks.

If you can find locally bred Guppies or even wild-caught ones, these are great choices for hard water communities, but the pedigree varieties produced on fish farms can be delicate, as can the more selected Platies. Mollies and Swordtails would be too big for your tank, but the Humpbacked limia, Limia nigrofasciata, is a pretty little fish with subtle colours and a sweet personality. It feeds primarily on algae but will eat flake food too, and if you keep a small group, you’ll find they generally behave themselves very well.

Most of your standard issue, farmed Corydoras catfish can handle water hardness up to 15˚dH without much trouble, and the tougher species like the popular Bronze and Peppered corys will do perfectly well up to 20˚dH. Likewise, you shouldn’t have any problems keeping bristlenoses in hard water. The Whiptail catfish, Rineloricaria lanceolata, is another splendid species that is much more concerned with having a sandy substrate and peaceful tankmates than it is over water chemistry. Hardier than it looks, it’s almost the perfect oddball for a small community tank, requiring little beyond the usual nighttime feeding that any catfish species needs to do well.

The hardy farmed danios can be expected to handle water up to 20˚dH without complaint, including Zebra and Pearl danios, both ideally suited to your tank. Some barbs will also adapt to hard water, including the Cherry barb, and with such charming colours and behaviour, it’s well worth considering for your tank.

Did you know?

Despite its name, the False penguin tetra, Thayeria boehlkei, is actually the most common ‘penguin tetra’ seen in the shops. There are three species in the genus, the other two being the true Penguin tetra, T. obliqua, and T. ifati, although they are rarely offered for sale. All three swim with the same head-up posture.