Hard Water and Aquarium Fish

Aquarium Fish Can Thrive in Hard Water

Guppies
Robert Pickett/Corbis Documentary/Getty Images

Hard water is a fact of life for most people. Unfortunately, many aquarium owners who have hard tap water are led to believe they must go to great lengths to soften their water before they can use it in an aquarium. After waging a losing a waging battle to adjust their water parameters, some fish owners give up entirely. That doesn’t have to happen to you.

Don’t Change Your Hard Water for Your Aquarium

Unless the fish you want to keep are the few species that absolutely require soft water to survive, there is no compelling reason to change your water at all.

That’s right -- don’t change the water parameters. It’s a slippery slope that invariably leads to heartache. Truth be told, constantly vacillating water parameters, due to ongoing use of water treatment products to alter water hardness and pH, are an even bigger contributor to fish stress than if the water were left in its natural state.

Don’t spit into the wind -- just accept your water the way it is, and choose fish that do well in hard water. There are plenty of them to choose from, and many are colorful and easy to care for. Which brings me to the next point…before you give up on your favorite fish, don’t assume they absolutely must have soft water.

Ignore the Fish Atlas About Hard Water

Don’t take everything printed in your handy dandy fish atlas as gospel. Not that those books are incorrect. However, there is an important difference between the data published in the fish atlas, and what is happening in the aquarium fish industry.

In the past fish were largely wild caught, but now many fish are captive bred, and they are not always bred in the exact same conditions as their native habitat.

Even though the atlas accurately states the original native habitat for a species of fish, it is quite possible the fish you bring home from your local pet shop wasn’t born or raised in that environment.

In fact, if your fish is one of the many species that are now commercially bred, odds are it was raised water that leans towards the hard alkaline side. As a result, many have so-called soft water species have been raised in, and become accustomed to hard water conditions.

Ask Your Local Fish Shop

Check with your local pet shop and find out what the hardness and pH levels are for their tanks. You may be surprised to find that most of their tanks are filled with hard, neutral to alkaline water, even though they are keeping fish that are supposedly soft water species.

Why would shops keep fish in the wrong kind of water? Because the fish were captive bred in hard water conditions, and it makes sense to keep them in water that is similar to what they were raised in. Add to that the fact that city water sources are usually hard, and it is no surprise that pet shops often keep their fish in hard water.

Hard Water Fish

You can bypass the whole issue of whether your fish will thrive in hard water, by simply choosing a hard water species. There are plenty of species to choose from, all of which will do quite nicely in that hard water from the faucet in your house. Here are a few popular freshwater fish species that are well suited to hard water conditions.

  • Livebearers – Guppies, Mollies, Platies, and Swordtails, including various crossbred species
  • Bettas and Paradise Fish
  • African and Central American Cichlids
  • Brackish fish – Archers, Monos, and Scats

Change Water Sources

Lastly, if your chosen species of fish truly must have soft water, you may want to consider changing water sources as an option, instead of using expensive ongoing water treatments. Reverse osmosis (R/O) water is one option, as is using a combination of tap and distilled water. Some industrious aquarium owners have been known to collect rainwater, which is naturally soft and acidic.

Ultimately, your best option for success is to follow the old rule of keeping it simple. Use the water you have, or can easily get your hands on. Don’t over treat the water with lots of conditioners, and choose fish that will thrive in what you have.