, , , , ,

How To Soften Aquarium Water Without Harming Your Fish

Products recommended in this post contain affiliate links. If you buy something through our posts, we may receive a commission at no extra charge to you. See our full disclosures here.

Do you have an idea of the dissolved minerals present in your water? Neither did I when I got my first fish tank. Luckily experiences, both good and bad ones have taught me a lot. So, are you dealing with hard water issues and not sure how to soften aquarium water? Check out this article for the answer.

Water hardness is a big concern for aquariums. There are two types of water hardness- carbonate hardness and general hardness. You can soften your aquarium’s water by the following:

  • Reverse Osmosis
  • Water Softening Pillows
  • Rain Water
  • Peat moss filter
  • Driftwood

Did You Know?

The water that lathers very easily with soap or cleansers is soft water. It contains few or no calcium and magnesium ions.


Properties of Hard water

Water that contains a large amount of dissolved minerals like calcium, magnesium and sometimes even manganese is “hard water”. Hard water may not be a health risk but surely is a nuisance due to the mineral buildup on fixtures, glass and poor soap and/or detergent performance. Dive in for some hard facts!

  • Hard water contains high amounts of mineral ions such as calcium and magnesium
  • Hard water is of two types, temporary and permanent.
  • Boiling can remove the temporary hardness of the water.
  • Permanent hardness needs chemicals to get soft water.
  • Hard water does not create much lather in shampoo, detergents, and cleansers.
  • When hard water evaporates, it leaves behind a chalky, white residue.
Quick and accurate- Recommended
  • easy to read color chart
  • Save time and get the test results within seconds
  • Simple and clear instructions make these hassle-free test strips super easy to use

How is hard water formed?

When water combines with carbon dioxide to form dilute carbonic acid, great solvent is formed. As water moves through soil and rock, it dissolves very some minerals in it. Calcium and magnesium dissolved in water are the two most common minerals that make water "hard."  The degree of hardness becomes greater as the calcium and magnesium content increases.

Did You Know?

Ipswich, a city in Australia has the highest levels of calcium carbonate in its water.

Methods for Softening Hard Water

Aquarium water hardness can be determined by the formation of limescale and patchy deposits on the glass. How to reduce water hardness in the aquarium has been a major concern for most aquarists. Softening hard water may seem tedious to you until you know the appropriate methods of doing it. Here’s how to soften aquarium water in five easy steps:

  • Reverse Osmosis

    Reverse Osmosis, commonly known as R.O is a process that demineralizes or deionizes the water to create a purer form of it. In this process, water is pushed under pressure through a semi-permeable membrane. The membrane blocks the larger molecules such as minerals and other contaminants present in the water.

    Reverse osmosis (RO) is being highly used to produce high-quality water. The R.O membrane blocks about 90 to 99 percent of the impurities present in the water. The purified water can easily be used in your aquarium.
​​Safer drinking water - excellent quality
  • Convenient, unlimited and refreshing
  • easy and hassle-free filter changes with no open sumps
  • Get clean and fresh-tasting water with fewer filter changes
  • Water Softening Pillows

    Another way to soften the general hardness of water is by installing a water softening pillow. You can place them in the filter of your aquarium for quicker results. These pillows contain sodium ions thus, replace the calcium and magnesium in the hard water with sodium. This method is most preferable for small tanks. 
​maintains a stable pH level - High Quality
  • Suitable for freshwater fish
  • scientifically proven to recude general hardness by lowering calcium and magnesium levels
  • can also be reused after it is recharged in a salt solution
  • Rain Water

    Rainwater is great water softening option for your aquarium. Moreover, this method is ecologically sound as well as inexpensive. However, you need to make sure that rain-water is clean. If you live in an industrial area with a considerable amount of pollution, avoid using rainwater as it will do more harm than good to your aquarium.

  • Peat Moss Filter

    You may choose a peat moss filter to deal with hard water. Place the peat moss granules inside the filter of your aquarium. Its mechanism lets the hard water goes through the peat before it comes back in the tank. You can also soak the peat granules in a container for about 2 weeks and then use the water in your aquarium. Just remember to keep the water aerated with an airstone. Do Not forget to boil the peat before usage. It is advisable to buy peat without any additives.
 enhance coloration and behavior - Best Value
  • all natural way to acidify aquarium water
  •  essential component for keeping and breeding tropical fish
  • Driftwood

    Using driftwood is a very good way to soften hard water. For the best results, you must use fresh and clean driftwood. You can boil the driftwood to get rid of any toxins or may even scrub it with a brush. They do not harm your fish but may render the water brownish. Hence, soak the wood in a container before placing it in the tank.
Perfect Fish Tank decoration - Best Choice
  •  safe for all pets
  • Adds natural beauty to aquariums
  • Ideal for both rainforest and desert terrariums

You must ensure that the aquarium water does not become too soft. Avoid keeping your fish in water that’s too hard or too soft because an excess of everything is bad!


Will Softening the Aquarium water harm my fish?

Softened water may not directly harm your fish, but the lack of minerals in it may make them sick. Soft water aquarium fish (where the water is too soft) might relatively be less healthy than hard water fish.

Further, most water softeners replace all the calcium present in the water with sodium. Certain fish species will not do well in this situation. You must research your fish and its soft water requirements thoroughly.

 Another option is to use potassium chloride instead of sodium chloride in your water softener. It is an expensive method though! Potassium is not as hard on the fish as sodium is. Moreover, if you have live plants they will absorb much of potassium to grow.

Did You Know?

Fish species like Livebearers, Central American cichlids and Rift Valley cichlids can mostly never adapt themselves to soft & acidic water conditions.

Risks and Benefits of soft water in an aquarium

An aquarium is undoubtedly a creative venture but has a technical side too. You must know things like whether your water is hard or soft and the pros and cons of both conditions.

1. Risks of water softening

It is generally assumed that soft water conditions in an aquarium are preferable for your fish. Up to a certain point, this is right indeed. But creating a highly-soft water aquarium can bring up an extra set of challenges for you!

  • The pH factor

    ​Soft is strongly unstable towards the pH than hard water. Aquariums can become more acidic over time, but in the case of soft water aquariums, this can happen very rapidly. Due to this, your fish may have to tolerate rapid changes in pH. Hence, you must do frequent pH tests and use chemical buffers while maintaining a soft water aquarium.

  • Pricey

    ​If you don't normally have soft tap-water on tap, converting hard water into soft water can be expensive. Certain chemical-procedures provide soft water, but at a price! Collecting rainwater may help, but getting pure rain-water is a task.

  • Seldom fish-friendly

    Domestic water softeners do not always produce soft water that is liable to be used in an aquarium. They simply replace limescale-forming minerals with minerals that don't form limescale. This is ok for your washing machines and dishwashers, but bad for your fish tank.

  • Reduces the efficiency of bacteria

    Filter bacteria work best in hard and alkaline water conditions. In very soft water that is acidic, filter bacteria may not work at all.

  • Excess of sodium ions

    Not all fish will do well in soft water conditions. Most of the water softeners soften water by replacing calcium and other minerals with sodium. This is somewhat similar to putting a goldfish in saltwater. This might kill the fish!

2. Benefits of water softening

It is generally assumed that soft water conditions in an aquarium are preferable for your fish. Up to a certain point, this is right indeed. But creating a highly-soft water aquarium can bring up an extra set of challenges for you!

  • Makes aquarium cleaning easy. Soft Water avoids limescale buildup.
  • Your aquarium appliances like filter and light last long in soft water.
  • Soft water turns out to be cost-effective in the long run.
  • Certain fish species do very well in soft water (unless the water is too soft and devoid of any minerals at all).

What Kind of fish Thrive in Hard water?

Refer below for fish species that do great in hard water.

  • Livebearer fish such as Guppies, Mollies, Platies, and Swordtails
  • Paradise Fish
  • African and certain Cichlids
  • Brackish fish like Archers, Monos, and Scats

Pro Tip

If you have hard water and do not wish to soften it, you can bypass the whole issue by simply choosing hard water aquarium fish species.

Video Introduction

On the whole

The field of pet care has had various opinions as to what’s right and what’s not. The same is with water softeners for the aquarium. Note that water softeners are not equally created and their efficiencies may vary. You must interrogate the manufacturer of the water softener on its risks and benefits.

It’s important to understand the tolerance levels of different fish. Their tolerance for water softeners may vary. Hence, you must confirm what and how much a particular fish species can bear in a given range of conditions.

Top Editor's Choice on Aquarium Water Softener

Subscribe to our Newsletter!

Join our mailing list to receive the latest tips and news of our blog.

Leave a Comment


Tips on How Often To Change Aquarium Water | Tips And Guides

How To Set Up An Aquarium Sump