Aquarium Water Hardness

The majority of aquariums are filled with Tap Water, which comes from ground water or streams-which also have ground water as their source. Actually ground water is rainwater that seeped through the soil to the deep subterranean layers.

Rainwater collects in the river or in ground water contains CO2, dissolving minerals and other organic substances from various earth and rock layers through which it passes and change the composistion of the water. Water in its natural form, has its own individual and particular properties depending on its origin.

The hardness of the water varies according to the type of rock layers the water passes through before gathering as ground water and how long the water is in the ground.

Aquarium water hardness can be classified as : [Note: in this article, we use German Degree to measure water hardness]

• Total Hardness (TH) / General Hardness (GH)
  Total/General Hardness is determined by calcium (Ca) & magnesium (Mg) ions dissolved in the water.
  1°dGH General Hardness (GH) = 5.5 mmol/liter alkaline earth (Ca & Mg) ions.
  Total/General Hardness is only becomes important when breeding fish from extremely soft water.
  Total/General Hardness category : 0-3°dGH = very soft ; 4-8°dGH = soft ; 9-12°dGH = normal ; 13-18°dGH = hard.

• Carbonate Hardness (KH)
  The calcium and magnesion ions referred above are not present in the water as pure ions, but as dissolved salt like Calcium or Magnesium Carbonate (CO3), Sulphate (SO4) or Chloride (Cl). The seperated quantity of Carbonates (CO3) is called the Carbonate Hardness.
  1°dKH Carbonate hardness (KH) = 17.9 mg/liter CaCO3. Why Calcium Carbonate (CaCO3) ? Since Calcium (Ca) is more significant than other elements (Mg,Na,K,Al,Zn,Fe) in most tap water.
  Carbonate Hardness category : 0-3°dKH = soft ; 4-8°dKH = moderate ; >8°dKH = hard.

The aquarium water hardness influences the organic functions of fish and plants. Fish and plants originating from soft water habitats do not thrive in hard water. Therefore, before buying pet fish, please check the fish orign waters. It's better to keep several species from similar water hardness habitats. For example : South American tetras prefer soft water, while African chichild prefer harder water.
However, plants and fish still can be kept well even in harder water, as long as other water parameters are kept at the best possible levels.

Note:

If you use Tap Water, the water contains a significant amount of trace elements and potentially harmful chemicals such as chlorine, heavy metals, phosphates, and nitrates! If your tap water is extremely hard or alkaline then it shouldn't be used for water changes without any treatment.
Therefore, it is wise to check & filter tap water before using it, you can use Water Purification filters such as Reverse Osmosis / Deionizer filter, UV Sterilizer and Ozonizer .
Or you can use Water Treatment Products such as Water Conditioner or Ammonia & Phosphate Removers as additives.

• Deionization or Reverse Osmosis filtration of tap water nitrates will help if your tap water contains significant levels of nitrates.
• Reverse Osmosis strips everything out of the water-the bad, but also the good. Healthy minerals are eliminated as the natural levels in water are altered and the water is now acidic!