How to soften Aquarium water hardness

How to soften Aquarium water hardness

Hey guys, just another blog by the World of Aquariums. Today, we will be talking about water hardness and how to soften your water in your aquarium. We will be giving a general run through of what water hardness is, why you might want to soften your water and the different ways of doing so.

For the full video guide, check out:


What is water hardness? 

Water hardness is how hard or how soft your water is and this is measured as gH, which stands for general hardness. Your general hardness will be purely made up of 2 mineral salts, which are calcium and magnesium. Unless you are using pure water, all water will have some amount of hardness, which can be measured using a gH test kit. For example, water with a gH of 3 degrees will be considered soft water while water with a gH of 10 degrees will be considered as hard water.

Why you want to soften your water?

It is true that most fish can adapt to a wide range of water hardness but there are still benefits or reasons you may want to soften your water.

The main reason is that the hardness of your water used to fill up your fish tank or perform water changes with, might not be suitable or in the correct range for the fish you want to keep. Most people will use tap water to fill up there tank and both general hardness and other parameters can vary quite a lot depending on their location. So, whilst someone else's water hardness from their tap are perfect for their type of fish, your own tap water might not be suitable for those same fish. Even if you live in the same city as someone else, your water parameters might be different. So basically, if your tap water is too hard, you will need to find ways to soften your water.

Secondly, some fish and aquatic animals are naturally found in very soft water environments or have less tolerance to hardness levels outside their suited range such as crystal shrimps and rams. By having soft water, this will replicate there natural environment and allow these animals to thrive, ultimately improving there health and colouration. The same thing goes with breeding, where having soft water will better induce breeding behaviour for aquatic organisms that are naturally found in soft water environments. 

Ways of softening your water

There are different ways of softening your water either during your initial tank setup or after your initial tank setup. And each of these will have either a strong or weak effect.

1: Substrate and Hardscape

Your substrate and your hardscape are things you add during your initial setup of your fish tank, which can help bring down the hardness. Both of these i would put as having a weak effect in softening your water and their effects will eventually get exhausted over time.

Substrates such as aquarium soils are used to create soft, acidic environments by retaining the mineral ions into the soil particles. As such, these substrates are commonly used for planted tanks. Most of the fish types that are chosen for planted tanks are also naturally found in soft water environments. On the other hand, most types of gravel are inert and will not effect the hardness of your water. However, other substrates such as coral sand will, and this will increase the hardness of your water and you definitely don't want to add this if you want soft water

For the hardscape, large pieces of driftwood slightly decrease the hardness of your water but will have a more significant effect in decreasing the pH of your water. These driftwoods will produce tannins and whilst it does make your water appear brown, it is completely safe for your fish. Some people will purposely sought out this look and these aquariums are called blackwater aquariums.


2: Change the type of water you are using

I would say this is the best method with the strongest effect, and that is to change the type of water you are using to fill up your aquarium itself. This can be switching from tap water into rain water, distilled water or RODI water, which stands for reverse osmosis deionised water. Rain water will always be naturally soft so definitely use this if you have a rain water tank. For RODI water, most aquarium stores will sell RODI water or the RODI unit itself, which will allow you to make it at home. Distilled water is quite similar and you can buy it from most supermarkets. If you have a large tank or multiple tanks, i will probably recommend investing in a RODI unit as they are very cheap in the long run.

The reason this is the most effective method is because it allows you to freely control what hardness you want your water to be at from the start. Also, if you are using very hard water for water changes, eventually it will use up the other methods you have added to soften the water. So for example, adding tap water with high gH will eventually exhaust the buffering capacity of soil. Please note if you are using RODI or distilled water you will to remineralize the water back or mix in some tap water as both will be completely free of general hardness, and even soft water fish will require some amounts.

3: Water softener pillows

The next thing you can do is to use products such as water softener pillows, which will have a strong effect in softening your water and decreasing your gH. These can be bought at your local aquarium store and can either be placed directly into your fish tank or filter. Essentially, these are just small pouches of deionized resin, which is one of the components for RODI filter unit. These pouches work, as the resin will absorb the calcium and magnesium ions from the water that passes through it and therefore, soften it.

4: Botanicals and additives

Finally, you can add Indian almond leaves or similar botanicals and blackwater extracts, which will slightly decrease the hardness of your water. However, these will have a stronger impact in creating acidic environments so I wouldn't recommend adding lots of these if you were after soft but alkaline water.

I hope this blog is helpful for anyone who wants to soften their water, as this is generally harder to do compared to hardening your water. 

For more related fish videos and guides, check out WorldOfAquariums youtube channel linked here:

1 comment

  • Leyna

    I have a 35 gallon aquarium and I recently found out I had hard water. I do have a water distiller but do you recommend going that route over all the other options you mentioned? Thank you

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