Daily Questions

Daily Question: What Fish Are Suitable for Hard Water.

Sue asks: What fish are suitable for hard water, especially for smaller tanks?

Ruth answers: It’s a question that comes up a lot, with the huge number of soft water fish from the Amazon and West African regions, and the large size of the Central American, hard water keepers can find themselves limited to the Rift Lake Cichlids, but do not despair, there are more out there.
For the purposes of this I’m referring to hard water as anything 7dGH and over, and very hard as 10dGH and over, but please check your water parameters and research the fish you are looking at.
I’ve deliberately avoided the three most common suggestions of Mollies, guppies, and plays.


This is a group of fish rather than a single species, but these little killifish are a fantastic starting point if you’re looking for a small species that thrive in hard water. Known as annual fish due to their fascinating adaptation. In the wild, they inhabit seasonal pools that dry up for at least part of the year. To stop this being the end of their species Nothobanchius practise live fast and die you, but their eggs can survive, and in fact need, a period out of the water.
Which means you can buy eggs, have them posted, wet them and wait for them to hatch. Watch out for scams online and head over to the British Killifish Association to source good quality eggs.
Do your research as there are the odd species that prefer softer water, but there are some great options.

Florida Flagfish Jordanella floridae

Want a fish that’s a bit like a Jack Russell in attitude, they think they’re a big huge fish, luckily they’re not. Getting to about 5cm, they’re a great option for water up to about 20 dGH. But they’re not a comfortable community fish, plan on keeping them alone, or with very carefully selected other fish.
Temp 18-30 degrees C
pH 6.5-8.5
Hardness 2-20 dGH

Wrestling Halfbeak Dermogenys pusilla

I’ve picked the Wrestling Halfbeak, but if you’re looking for a micro predator that looks like it should be about 5 foot long, but is about 5-7cm, have a nosy around the Halfbeaks.
These guys tend to hover just under the surface of the water and can take very hard and even slightly brackish water, but make sure you keep your water spot on, as they don’t take poor water in any shape or form.
Temperature 24-28 degrees C
pH 6.5 -8.0
Hardness 10-20 dGH

Pike Topminnow Belonesox belizanus

Dreaming of owning an alligator gar or arrowana, but don’t have the space. Well there is a little liver bearer that’s well worth a look. The Pike Topminnow aka the Pike Top Livebearer is something to have a good look at.
A wonderful aggressive character the females will get to about 15cm so don’t plan on keeping these in a tank smaller than 90 or 120cm, but they can take a huge range or parameters, but they thrive in more alkaline and harder water. Keep them as a species-only tank, or with very carefully researched larger fish. But these have to be a great choice if you have the right water for this sort of live bearer but don’t want colourful guppies.
Temperature: 25-37 degrees C
pH 6.0-8.0
Hardness 9-19 dGH.


Photo credit Adam Jones https://creativecommons.org/licenses/by/4.0/

Another group of fish, but so many of them thrive in hard water, livebearers, but never fear, they’re not as good at having offspring as Guppys and Mollys, and there is normally a home available for any excess offspring. A favourite of mine is the Butterfly Splitfin, Ameca splendens. Thriving in pH 7.0-8.0 and a hardness about 10 -20 dGH. Have a look through the lists of goodieds and see if there is something that catches your attention.

White Cloud Mountain Minnows. Tanichthys albonubes

An aquarium favourite there are various colour strains, and they’re readily available. I wouldn’t keep them at the top of their range as in the wild they’re often found in blackwater habitats, but they’re a great addition to a tank. Make sure there is nothing big enough to eat them and give them enough space to swim.
Temperature 14-22 degrees C
pH 6.0-8.5
Hardness 5-20 dGH

I could go on, but here is a little list of a few more ideas
Paradise fish, super adaptable, so don’t discount them.
Hillstream loaches. Want a hard water river tank? These are great.
Rainbow shiners. Not for a little tank, but a great hard water choice.
Rainbows. Again not for a tiny tank, but worth an upgrade.
Danios: they need swimming space, but again some hard water lovers in there.
Shell dwellers: if these guys had legs, they’d take over the world, hard water rift lake cichlids, but in teeny tiny bodies. Give them enough space to establish territories and enjoy watching the chaos.

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Ruth McDonald

Sailed twice around the world, started my acedemic career as an archaeologist and somehow ended up lecturing on science and researching fish.

Tropical Fish Keeping UK