Understanding Water Hardness in The Aquarium

When it comes to water parameters in the aquarium there is probably no parameter thats more important than water hardness. But what is it? In fact, there are two types of water hardness to understand, General Hardness(GH) and Carbonate Hardness(KH), both very important. So whats the difference you ask? Read on to learn more about understanding water hardness in the aquarium.

Water Hardness in the Aquarium

General Hardness

General Hardness is often referred to as total hardness, its the measurement of mineral salts in the water, most often Calcium(Ca) and Magnesium(Mg).

For cell growth in any living organism, be it plant or animal, calcium and magnesium are the two most important minerals. In the Aquarium, fish and plants most often assimilate these directly from the water. Without GH in the water we often see deformed leaves and slow growth in plants and poor health from fish, often stunted growth.

Additionally, GH is also important for invertebrates like Dwarf Shrimp, Crayfish and Snails for the development of their shells.

For most plants, a GH of 4-8dH is adequate for sustainable growth. Some fish like African Cichlids, Livebearers and Goldfish will enjoy a higher GH value.

Also, another reason that GH is important in the aquarium is due to its effects on a fishes ability to ‘osmoregulate’. Osmoregulation by definition is a process that regulates the osmotic pressure of fluids and electrolytic balance in organisms. It is the reason fish need to be acclimated to any new water parameters. Fish will regulate their internal salt/mineral content to match the water in which they are being housed in. When we move a fish to a differing GH the fish will need to match the new water GH parameter otherwise may succumb to osmotic shock. This is the most common cause of fish death when customers take home fish and they die soon after being added to the new environment.

How do we Measure GH Water Parameters?

We measure aquarium water GH in either dH(degrees hardness) or ppm(parts per million). 1 degree of GH is equal to 17.9ppm. The most common way to test for GH is a titration test which are very easy to use.

Below are the values of GH and how they correlate to one another.

0-4dH(0-70ppm) – Extremely Soft.

4-8dH(70-140ppm) – Soft.

8-12dH(140-210ppm) – Medium.

12-18dH(210-320ppm) – Hard.

How do I Raise my General Hardness in my Aquarium?

In our store we use a few different ways to raise our General Hardness in our aquariums. For instances where we would like to raise the GH on its own we use Continuum GH+. In other instances we can use some crushed coral in the filter or substrate to raise the hardness. It must be noted though that the crushed coral is comprised of calcium carbonate, as a result, the Carbonate Hardness(KH) and PH parameters will also be affected.

Aquarium Water Parameters

Carbonate Hardness

Carbonate Hardness can also be referred to as temporary hardness and can also be called total alkalinity. It is the measurement of bicarbonates and Calcium Carbonate(CaCO3) in the water.

In the Aquarium, maintaining a healthy KH is paramount for keeping the aquarium stable. By definition Alkalinity is the water’s capacity to resist changes in pH that would make the water more acidic.

Organic substances like fish waste, driftwood etc are naturally acidic and will in time cause the PH to drop in the aquarium, the KH acts as a buffer, preventing this from occurring too quickly in between water changes and aquarium cleaning practices.

A KH of 4dH is generally what is considered stable and will go a long way in preventing fluctuations oh PH parameters.

KH and PH Relationship

Many times people assume KH and PH to be the same thing, although related, as explained above they are not the same. While often times a high KH will also coincide with a high PH, a low KH can also coincide with a high PH if there is anything alkaline based in the water because water with a low KH has low buffering capacity, it takes very little to sway the water each way.

How do we Measure KH Water Parameters?

We measure aquarium water KH in either dKH(degrees carbonate hardness) or ppm(parts per million). 1 degree of dKH is equal to 17.9ppm. The most common way to test for KH is a titration test which are very easy to use.

How do I Raise my Carbonate Hardness?

To raise our Carbonate Hardness in our aquariums we use Continuum KH+. As noted above, in other instances we will use crushed coral to raise the KH in the water as it dissolves. Again, it must be noted that this route will also raise the General Hardness and PH of the Aquarium at the same time.

2 thoughts on “Understanding Water Hardness in The Aquarium

  1. Can there be such a thing as too hard of water?
    I have tried to just top off my water, but i find my GH and KH increase over time.

    Found your website via your feature in the keepingfishsimple youtube channel.

    California, USA

    1. Hi Brice,
      Water GH can increase over time as foods etc will contain calcium and magnesium. KH and Gh can increase slightly as it does slowly leech from rocks and sand within the aquarium. Also topping off with water that isn’t RO water will increase slowly as only pure water will evaporate.

      I hope this helps.

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