How To Make Aquarium Water Soft? (Foolproof Ways)

Image of an aquarium with soft water

There are various ways to soften the hard water. You can use reverse osmosis or water softening pillows to make the aquarium water soft. Peat moss and submerged driftwood will also help to soften the aquarium water. You can also use rainwater in your fish tank since it is pure and naturally soft.

Let’s understand this in more detail now.

Understanding Water Hardness

Water hardness is caused by the presence of dissolved minerals and salts in the water.

Water in its pure form is called soft water. Soft water does not contain minerals like calcium or magnesium.

It will also be free of carbonates. However, when these naturally occurring minerals are present in the water, it becomes hard water.

When you boil hard water, it leaves a white chalky residue behind.

The presence of minerals and salts in water also causes scaling in kettles and scums in baths and sinks.

You can confirm that the water in your locality is hard water if you notice these scales and scums.

Nonetheless, it is best to use a testing kit to measure the hardness level accurately.

A hard water testing kit will also allow you to obtain the pH measurement of the water and adjust it suitably.

The hardness level of water depends on the amount of salt dissolved in it.

It is usually described using two relative terms:

  • General Hardness (GH), and
  • Carbonate Hardness (CH).

General hardness describes the amount of calcium and magnesium dissolved in the water.

Many fish find it difficult to survive in water with high GH levels.

Meanwhile, carbonate hardness measures the presence of carbonate and bicarbonate ions in the water.

The pH of water is closely linked to carbonate hardness.

You must monitor the carbonate hardness to maintain a constant pH in your fish tank.

Why Should You Soften Your Aquarium Water?

Most aquarium pets tolerate moderately hard to soft water.

However, a few varieties, like cichlids, guppies, mollies, and swordtails, can live in hard water.

You can keep these fish in hard water.

But fish and other aquatic creatures that need soft water will find it difficult to adjust to a hard water tank.

The presence of minerals and salts in the water will affect their osmoregulatory balance.

Any changes to the osmotic balance will cause stress to the animals. Over time, it can even lead to their death.

Hence, you should understand the requirements of your aquatic pets and adjust the water hardness of their surroundings to help them thrive.

Ways To Make Aquarium Water Soft

There are various ways in which you can soften the aquarium water to suit the comfort level of your pets.

Nonetheless, always change the hardness level of aquarium water gradually and continuously.

Sudden changes are detrimental to the health of your aquatic pets.

As a responsible pet owner, you should frequently monitor the hardness level of your aquarium water.

It will allow you to fix any changes before it adversely affects your pets.

There are four ways to prepare aquarium water for your tank.

  1. Either soften tap water before adding it to the tank by using:
  2. RO Filter, or
  3. Water Softening Pillows.
  4. Use suitable agents to soften the water that is present in your tank by using:
  5. Peat Moss, or
  6. Driftwood.

Let us explore how these options work.

How to Make Tap Water Soft For Aquariums?

You can reduce the hardness of tap water by using an RO filter or water softening pillows.

Reverse Osmosis (RO) Filter

RO filters force hard water through a permeable membrane under pressure.

The filter blocks minerals and contaminants. This allows clear water to pass through.

The advantage of this method is that it does not use any chemicals.

RO effectively removes 95% or more of dissolved minerals. However, RO filtration is time-consuming.

It also makes the water very soft by stripping it of all minerals.

So, it will remove the useful trace minerals you’re your fish need, along with the salts and carbonates.

You may have to mix RO water with tap water to adjust the pH if you prefer water with moderate hardness.

Water Softening Pillows

Water softening pillows reduce the hardness of the water by using ionized filtration media.

When you pass tap water through a water softening pillow, the reaction with the chemical in the filter media makes the calcium and magnesium levels decrease.

Thus, the water becomes soft.

You can add water softening pillows to your filter to make the process easier.

However, water softening pillows will raise the sodium level of the water.

Hence, this method is not as desirable as the RO filter for softening aquarium water.

How To Soften Aquarium Water When It Is Already In The Tank?

If the pH level of the water in your aquarium increases, you can fix it without having to empty the tank.

In this case, you can use either peat moss or driftwood in the tank to soften the water.

Peat Moss

Peat moss binds to calcium and magnesium ions in the water.

It will also reduce the carbonate level of water by releasing gallic and tannic acid, which break down bicarbonates.

The easiest way to add peat moss to your tank is to add it to your aquarium filter.

As the water cycles through the filter, it will become soft.

Another way to use it is to stuff peat moss in a cloth cover or case and submerge it in your tank.

You can also pre-treat aquarium water with peat moss for two weeks and transfer it into the tank when you perform a water change.


Driftwood works just like peat moss. It releases tannins into the water that breaks down bicarbonates.

You can simply add it into the tank and leave it to do the job. Due to its natural look, it will also look good in your tank.

However, driftwood will change the color of the water.

This is a normal reaction and will not harm your fish in any way, although the water will look dirty.

Nonetheless, you should be careful when adding driftwood to a tank.

Dirty driftwood introduces harmful parasites into the tank.

So, clean it thoroughly to eliminate contaminants before adding it to the tank.

Is Rainwater Safe To Use In An Aquarium?

If you are looking for an inexpensive option for soft water, rainwater is a good choice.

Properly harvested rainwater is clean, free from toxins, and soft.

If you live in a place where it rains frequently, you can collect rainwater and add it to your fish tank.

Just make sure that you use clean containers for the purpose.

How To Soften Aquarium Water For Shrimp?

Some varieties of shrimp, like cherry shrimp and armano shrimp, can live in moderately soft to hard water.

However, tiger shrimp and bumblebee shrimp will perish if they are placed in hard water.

You will need soft water if you intend to keep these animals as pets. Home water softeners may not be effective in this case.

Since shrimp are tiny creatures, any sudden changes in the water chemistry affect them drastically.

The best way to soften aquarium water for your shrimp is by using peat moss or driftwood.

Some shrimp owners also recommend adding shrimp to a mature tank that is already stabilized with RO water.

Sudden changes to the water chemistry will send the shrimp into shock.

However, when you add them to a mature tank, they adapt sooner because the water is stable.

Nonetheless, you should continuously monitor the water hardness to ensure it is within the permissible range.

How To Soften Aquarium Water For Discus?

Discus fish are not very easy to maintain as they are sensitive to even the smallest changes in water chemistry.

Most discus varieties only survive in soft water.

Discus requires soft and slightly acidic water.

Since these fish are very sensitive, the water hardness level of their tank should always be under control.

You can soften aquarium water for discus using a reverse osmosis filtration system.

The RO system will strip the water of any magnesium and calcium salts as well as clear the carbonates in it.

If the tap water in your area is soft, you can use it in your discus tank after passing it through a carbon filter.

European-bred discus is an exception to the rule. These fish have adapted to hard water.

They will survive and even breed in hard water.

However, wild discus and Asian discus cannot adjust to hard water environments.

Check with the supplier from whom you buy your fish to understand their exact water chemistry needs and prepare their aquarium accordingly for the best results.


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