Water Softener vs Water Filter – What’s the Difference?

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Your aquarium water quality impacts directly the health of your fish. The presence of minerals such as calcium and magnesium will not only result to build ups that impair the clarity of your water but also an alteration in key parameters such as pH concentration.

When addressing the effects of both smelly and hard water, two key accessories come in mind. These are; water softeners and water filters.

These two equipment can be used concurrently in maintaining quality aquarium water.

However, the fact that these two devices are being used concurrently doesn’t mean they are the same.

Water Softener vs Water Filter
Water Softener vs Water Filter

In this article, we are going to show you what the two devices are,  their differences and whether you can use them in your aquarium.

Water Softener Explained

Water softening refers to the art of removing mineral ions such as magnesium and calcium from the water. Any water that has a significant amount of calcium and magnesium ion is referred to as hard water.

A water softener refers to the equipment or appliance used in the process of water softening.

Oftentimes,  it uses the process of reverse osmosis to draw mineral ions from the water without any significant alteration in its quality and amount.

Generally, water softeners are categorised into four types depending on how they operate. These are:

Ion-exchange softeners

Most of the softeners that you see around homes are usually ion-exchange softeners. These appliances work by substituting the hardness (calcium and magnesium ions) with soft ions such as Potassium and Sodium.

Ion exchange softeners come with a resin tank that contains small beads covered in salt ions.

As the water passes through the resin tank, calcium and magnesium ions are attracted and deposited in the tank through either a Demand Initiated Regeneration or Time Initiated Regeneration.

Salt-free softeners

Salt-free water softeners do not remove calcium and magnesium ions from water. Rather, they crystallize the ions into a form that is not attachable on surfaces such as water pipes. This process is known as water conditioning.

Reverse osmosis system

Reverse osmosis system filter the water. They remove the magnesium and calcium ions plus other contaminants such as lead, salt, pesticides, nitrates and fluoride using an installed filter.

Magnetic softeners

These types of water softeners remove calcium and magnesium ions from water by passing the water through a magnetic field.

As the liquid passes through the field, the two ions are attracted to one side of a magnetic pole hence leaving clear water to flow through.

Do You Need a Water Softener for Your Fish Tank?

Aquarium fish species come from different biological backgrounds. Some thrive in hard water. Others thrive in soft waters. However, in as much as many species of fish come from soft water areas they ideally thrive in hard water.

So, before answering the question of whether you should acquire a softener for your tank, it is prudent to know the quality of water that suits your pet.

Species such as Betta fish, Tetras, Bars, Corydoras Catfish and Angelfish Catfish are from soft water environments. Ironically, they survive better in hard water.

On the other hand, species such as American Cichlids, Livebearers and Rift Valley Cichlids will never adapt to a soft water environment.

Soft water aquarium is only of help in two crucial circumstances. First, aquarium species such as Tetras and American Dwarf Cichlids will not spawn in a hard water aquarium.

However much happier they will be, improper water chemistry cannot allow for the development of their eggs. As a breeder, this means you must soften your water to obtain fries from your pets.

Secondly, certain species of fish such as Chocolate Gouramis, Rasboras and Wild-caught Discus will not survive in hard water. To keep them alive, you must keep the water soft enough.

How to Soften Aquarium Water?

Rainwater is the first-hand alternative for softening. Though it comes with other problems, it is highly economical and readily available in some parts of the world.

However, if you cannot afford to collect rainwater, the only option is softening. But, there is a lot to this.

First, the readily available domestic salt-based softeners are not suitable for aquarium water. As said prior in the article, they only substitute magnesium and calcium ions with sodium or potassium ions.

In as much as they will protect your tank from seasoning, they can easily cause a spike in the pH.

On the other hand, reverse-osmosis softeners are expensive. These devices are also very slow and have limits as to how much water they within a given time-frame.

However, once you have installed the appliance, you should be ready to reap the wide range of benefits attached to using soft water in your tank.

Cons of Soft Aquarium Water

The fact that you can soften your water does not mean you will turn victorious. In reality, one evident problem comes with using soft water for your aquarium tank.


The problem of acidification is prevalent in almost all tanks. It results from processes such as nitrification, respiration, photosynthesis and presence of Bogwood and Peat in the tank.

In hard water, a spike in pH is hard to come about. This is because of the presence of various acidic, neutral and basic ions that tends to naturally balance out. Bicarbonate, carbonate, hydroxide and some other mineral ions tend to raise the pH.

On the other hand, Nitrates, Carbon dioxide, Bogwoods and Peats in the tank tends to lower the pH.

Soft water contains negligible amounts of dissolved minerals. Its alkalinity reserve is lower as compared to hard water.

Therefore, whenever there is an accumulation of nitrous waste and ammonia, the system will lack defensive basic elements to balance it out. As a result, the pH spike will be tremendous and endangering.

Water Filters Explained

Water filters are one of the essential accessories in an aquarium tank. These systems can either be purchased separately or bought as part of an aquarium kit.

In a fish tank, filters are used to remove impurities in the form of particles, toxic chemical contents and bacteria. Unlike softeners, these accessories do not remove magnesium and calcium ions from water.

Aquarium filters come in a wide range of types and designs. Generally, there is no do-it-all type that will suit all your needs at once. The most common types of aquarium filters include:

Mechanical Filters

Mechanical filters trap particles consisting of uneaten food, decaying matters, fish wastes and other debris from aquarium plants. In an aquarium setting, they come as the first media.

The type of mechanical filter used in a specific tank matter a lot. Some filters promote colonization of beneficial bacteria in the aquarium while some do not. Common types of mechanical filters include:


Sponges are made up of openings that allow for the filtration of small debris inside it. Some come with medium-sized pores while others come with small-sized pores. How efficient a sponge filter primarily depends on its pore size.


Pads are common filters in canisters and other power filters. They come in square, rectangular and circular shapes. Just like sponges, they also come in a wide range of pore size to suit different purposes.

How porous the pad determines how efficient it is and how often you will need to de-clog it.

Filter Floss

Old-age tank boxes came with filter wools that were stuffed inside them to capture debris inside the aquarium. The same concept applies to date. In the modern age, filter floss is used in canisters and wet/dry sumps.

Some trickle filters also feature these materials.

Biological Filters

These types of filters are used to break down different bacteria inside an aquarium tank. They enable bacterias to colonize and propagate to break down wastes that call for the manifestation of beneficial bacteria.

Biological filtration in an aquarium tank prevents ammonia spike. Any resultant waste that generates ammonia is broken down into nitrites which are usually less toxic as compared to nitrates. This biological process is called the nitrogen cycle.

To understand how biological filtration process works, you must lucidly understand the nitrogen cycle.

However, condensed into a paragraph, this process occurs due to the help of a bacteria called Nitrosomonas. In the presence of dissolved oxygen, Nitrosomonas bacteria consume Ammonia and convert it into relatively harmless Nitrites.

Chemical Filters

Chemical filters remove the invisible and dissolved chemical compounds found in aquarium water. It removes what cannot be removed by physical process.

If you have ever been keen on some aquarium, then you must have come across yellowish aquarium waters. Usually, this is because of the high concentration of organic substances that results due to the long-term accumulation of chemical compounds.

As far as the compounds are concerned, low accumulation may not be lethargic to the health of your fish. They only become deleterious under high concentration.

Chemical filters inhibit their concentration for a quality aquarium environment.


The difference between softeners and filters greatly lie on their use. Whereas filters can be used to softening, softeners cannot perform the wide range of duties that filters do.

Otherwise, in the same tank, you can install three different types of filters to achieve the desired quality of aquarium water.


This is George, the Aquaman, editor at AquaMantra. I'm a water quality analyst by profession, and used to work at one of the largest water bottler company.
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