Aquarium Water Hardness

Aquarium Water Hardness is often talked about by aquarium keepers but not acted on. It actually has quite an effect on both the fish and plants that you keep so it is worth learning about water hardness.

So what is aquarium water hardness and how does it affect you. Water hardness is about the amount of dissolved minerals in water. It is important to you because each fish and plant has an optimal range of water hardness in which they thrive. Move too far outside this and your fish or plants will suffer.

In a fish’s natural environment the water hardness will be determined by their environment.  If they live in a stream that is fed by run off from limestone and some other rocks there will be a higher mineral content adding hardness to the water.  If on the other hand they come from a forested area with dense vegetation they are likely to thrive in soft water.

Your home water supply hardness will be determined in the same way.

There are two approaches to managing aquarium water hardness.  Both work but one requires more work than another.

If you are new to aquarium keeping simply check out your local water supply to determine its natural hardness and pH levels and then simply choose fish and plants that fit the type of water that you have.  You will always get a good choice from your local pet store as they probably are using the same water as you. (local tap water).  The plants and fish that we have recommended generally do well in a wide variety of water conditions.  Your work here is around researching fish and plants to make sure that they suit your local water conditions

If you are going to manage the water hardness in order to keep a wider range of fish then you need to understand more about the science behind the water.  This is a huge subject that involves a fair bit of chemistry.  We simply try to cover the basics here to get you started.

  The total hardness of water is a measure of the amount of minerals that it contains and is made up of two different measures.

Temporary hardness is a measure of the level of carbonate or bicarbonate ions in the water and is measured on the Kh scale.  If your water has a Kh reading of 3 or more it will have a strong buffering effect on the water.  Buffering is the ability for water to resist changes in the pH levels, so the carbonate level is directly related to the pH level.  It is called temporary hardness because the carbonate ions can easily be removed from the water through boiling and are therefore seen as temporary.

General hardness of Gh is the measure of other ions, primarily calcium and magnesium. 

Aquarium Keepers tend to talk in terms of dH which is an overall measure of water hardness.  You will usually find that fish and plants have recommended dH parameters which they are best kept in.

Controlling dH is the challenge.  It is far easier to increase water hardness than it is to decrease it.  This can be done by adding rocks or decorations to the tank that leach salts over a period of time.  Limestone is an example of this.  You can also get filter inserts and chemicals that will do the job for you. 

Decreasing water hardness can be done by using de-ionised water or rainwater to dilute your tap water.  Care should be taken if using rain water in areas of high air pollution as this may change the chemistry of the water.

It is far easier to have your tap water tested and then stick to fish that fit the water, certainly when starting out in the aquarium keeping hobby.