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Aquarium Water Hardness Test

Water Hardness is an important measurement, which you need to establish and maintain in your aquarium especially when it comes to community tank whereby there are different species of fish living in it. Generally the numbers indicated by water hardness represents the total amount of dissolved mineral content primarily calcium and magnesium. It is usually expressed in units of ppm (parts per million) and another in terms of water General Hardness (dGH). These figures vary considerably depending on the source and supply of water to different areas of residence and individual states.

Aquarium water hardness is generally classified as either hard water or soft water. Depending on which types of fish that you have in your tank, each individual species has different requirement that falls within certain range limit. For ease of reference, I’ve come up with a table below that indicates which group of fish belongs to what level of water hardness so that you can use it as a guide when setting up your aquarium tank. The task become trickier when it comes to community aquarium because basically what you need to do is to find out and establish a range of hardness level whereby all species can tolerate well in it.

Water Hardness Chart for Different Aquarium Fish Species

Hardness (dGH)Hardness (ppm) Definition
Types of Fish
1 to 3.517.1 to 60very soft-
3.5 to 6.760 to 120softAngelfish, Neon Fish, Goldfish
6.7 to 10.0120 to 180hardDiscus, Hatchet Fish, Oscar, Betta, Swordtail, Guppy
10.0 and above180 and abovevery hardDemasoni Cichlids


In order to test for the water hardness level in your aquarium water, there are different water test kits and equipment you can use to get an accurate and fast measurement. Some of the easiest method is to use test strips whereby the color indicator will change according to different levels and then compared to a scale of colors in order to get the reading. Others like digital hardness meter reader are far more convenient because it can give a direct reading by just dipping the probe into the water. What makes a difference between those two methods are basically price factor in which strips are much more cheaper while meter readers cost at least 10 times more.

Nowadays adjusting aquarium water hardness is a breeze because basically there are many options available. Based on the reading and measurement obtained earlier, all you need to do when you find out that the water is too hard is to purchase some water softener pillow from pet shops and place it on your aquarium filter media. Basically what the pillow does is that, it will lower the water hardness level by absorbing and then removing the calcium and magnesium content from the water using the ion-exchange concept. On the contrary, if you find that the water is too soft, then all you need to do is to add in mineral salt, which is easily available in your local fish center. However, I do not recommend using crushed corals for the purpose of adjustment because the fluctuation in levels and release of minerals can become uncontrollable and instead ended up with water that is too hard.

Further reading: Using pH test kit to maintain perfect water quality



comparison between fluval and eheimComparing Between Different Fish Filters (Advantages and Disadvantages). How about other brands like the BiOrb?

About Me

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My fascination and interest towards aquarium fish has led me to devote my time towards caring and learning about this wonderful pet.

Aquarium fish keeping is a very challenging and exciting hobby. When I first started, I never knew much or have the necessary guidance back then because none of my family members were actually a keen hobbyist. And because of that, I’ve encountered numerous failures and the worst part is having to deal with dead fish every time when you started to grow fond and getting attached to my pets. However, I persevered and took steps to find out and search for information from other hobbyist, apart from the knowledge gained and learned from my own experience and research. The blog that I’ve created here is meant to share useful information and tips about aquarium fish keeping so that new hobbyist will not make the same mistakes that I’ve made in the past."

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