How does pH, GH & KH affect your aquarium?

How does pH, GH & KH affect your aquarium?


Chemical importance in aquariums

Whether you are a beginner or expert fish keeper, it is important to understand basic ideal water conditions for your home aquarium, so your fish stay healthy. It is especially important in the weeks before you introduce your fish into a new environment from the fish retailer. You need an understanding of waste so that your aquarium stays clean and maintains a stable environment. Testing kits such as API is recommended for every fish keeper, and it is a good habit to regularly test the water to catch any problems before it is too late. Conditioning the water in your aquarium is essential for both fish and the beneficial bacteria that builds up. Every time tap water is added you will need to de-chlorinate it.

pH, GH and KH are all measures of ions which are important to control in your fish’s aquarium, they are referred to as the ‘Bermuda Triangle’ of water chemistry which means if you change one, the others are likely to change too.

pH (Power of Hydrogen)

pH measures the acidity or alkalinity of your aquarium water. The ‘H’ refers to the hydrogen ion content, the lower amount of hydrogen ions the more acidic a liquid is, and vice versa. The scale runs from 0-14.0, 7.0 being neutral. Every number on the scale is ten times greater than the previous number. pH plays a big role in how comfortable your fish will be in an aquarium.

Fish thrive best where the pH is the same as their natural environment. Some aquarium fish prefer a low pH environment. For example, emperor tetras and South American characin fish have a tolerance to low pH due to their environment in the wild.  They can be kept at a water pH of 3.5 however most fish cannot tolerate such low levels. For example, koi prefer a higher pH between 7.5 and 8.2, therefore ideally your aquarium should be neutral when keeping different varieties of fish.

Over time the pH in an aquarium drops, adding rocks and calcium-rich sediment is a natural way to raise pH which is why lime sand and coral grit is great. To control the pH of the water, regular pH water test kits should be carried out. Everywhere the chemistry of tap water is different, if you live in an area with hard water it is likely the pH will be high, adding a buffer and water softener will neutralise it.

Another issue is ammonia, which if increases can be very toxic to fish. Toxicity increases as pH and temperature increases. When the pH of aquarium water reaches 9.0 the ammonia in the water is converted into very toxic ammonia killing everything in your aquarium, even your plants. This also causes respiratory problems in the gills and kidneys, affects growth, and makes the fish more susceptible to diseases.

To increase the pH, the use of aerosols is the cheapest and fastest method.  Additionally, pH can be easily increased by adding baking soda into the water. It is advised to mix 1 teaspoon of baking soda for every 18 litres. However, do not forget to remove your fish before raising the pH. To decrease the pH filtering peat moss is the most effective but you can also increase the amount of carbon dioxide.

GH (General Hardness)

This is the hardness of your aquarium water, which is affected by calcium and magnesium ions. Some fish species like ‘hard’ water with a high GH, and others ‘soft’ water (low GH). Ideally, freshwater aquariums have a GH of 4-8 dGH (degrees of GH), but it is important to research the specific species before setting up your aquarium. If you are into breeding your fish, the water hardness should be kept softer as fish generally breed during the rainy season where the GH drops. Goldfish and African cichlids are ‘hardy’ fish and prefer water with a higher GH level.

Maintaining a healthy GH is important for muscle and bone development, moulting if you have shrimp, shell development in snails and plant growth if you are keeping live plants in your aquarium. A low GH water quality can have significant effects on your fish. Lookout for fish with a slow growth rate, loss of appetite and acting lethargic as these are signs of low GH.

Increasing the GH is easy, just place some seashells and coral into the tank or add limestone into the filter. Decreasing the GH is a bit more work, you are best to start by introducing reverse osmosis (RO) water when you do a water change. It is chemical-free, has a neutral pH and has no water hardness, so it will not affect the other properties in your aquarium. 

KH (Carbonate Hardness)

This refers to the number of carbonates (CO­3) and bicarbonates (HCO3) dissolved in your aquarium water which affects the buffering capacity. The buffering capacity is important to keep the pH stable as fish cannot tolerate shifts in pH as mentioned above. A low buffering capacity means a low KH and the pH is easily shifted, however, a high buffering capacity has a high KH, so the pH does not change as easily. KH is measured in degrees of KH (dKH) or parts per million (ppm). It is recommended a freshwater aquarium is kept between 4 dKH (71 ppm) and 8 dKH (143 ppm). African cichlids are a typical example of fish that thrive in a high KH environment greater than 10 dKH, but most fish cannot tolerate this.

To lower the KH you can add a buffer. This involves mixing distilled and tap water or adding Indian almond leaves. To increase the KH you can directly add substances such as crushed coral, aragonite, or dolomite rock.