Water is water, right? Well, not exactly. You can’t see them, but water contains various organic and inorganic molecules and compounds that can be both harmful and beneficial to your fish. This guide explains the basics of aquarium water chemistry and why regular testing is so important.
What’s in Water?
Pure water is made of just two chemical elements: hydrogen and oxygen. However, this clear inorganic compound can carry all manner of other organic and inorganic matter. The types and amounts of particles dissolved or suspended in water vary between water sources and are influenced by a number of factors.
Water dissolves salts when it flows over some types of rocks and soil, so rivers and lakes in certain areas have a higher mineral content than others. Organic materials also affect water, so the amount of plants and animals that live in and around a water source will also alter water chemistry.
Testing Aquarium Water
Water chemistry can be pretty stable or swing dramatically from one day to the next. Aquariums are much smaller than ponds, lakes, and rivers, so they tend to be a lot more unstable. Your goal as a fish keeper is to keep your aquarium clean and prevent water chemistry from fluctuating or becoming toxic to your fish.
Aquarium water test kits provide a reliable solution for monitoring your water chemistry, so every fishkeeper should have one. In fact, water testing is one of the most essential tasks for a clean and healthy aquarium.
Beginners often prefer strip tests that measure various different parameters. These five-, six-, or even seven-in-one tests can measure all of the variables mentioned in this article and provide an affordable and easy-to-use solution. Liquid test kits are more precise, but also a little more difficult to use. They can be bought in a set or individually.
Now that you know the basics of water chemistry and why testing is so important, let’s dive in and examine some important water parameters.
Ammonia, Nitrite, and Nitrate
The nitrogen cycle is one of the most important concepts in the aquarium hobby. Unfortunately, many new fishkeepers buy their first fish without understanding this process, sometimes with disastrous results!
Decaying organic matter like fish food and fish waste releases ammonia into the water. This nitrogen compound is toxic to fish, but special bacteria quickly convert it into another compound called nitrite. Nitrite is not much better for your fish, but this is soon converted into a third compound called nitrate, which is safe for fish at low levels. Nitrates will usually increase over time and the best way to remove them is by performing water changes.
Most of the special bacteria responsible for maintaining the nitrogen cycle live in your aquarium filter, so this is one piece of equipment that every fish tank needs. Read this guide to learn how to choose the right filter for your small fish tank.
Ideal test results:
- 0 ppm ammonia
- 0 ppm nitrite
- Less than 20 ppm nitrate
Chlorine
If you use municipal water, there’s a good chance that you’ll detect chlorine when testing your water. Chlorine and chloramine are chemicals that disinfect water to make it safe for human consumption. Unfortunately, these chemicals are also bad for fish, so it’s important to test for them and neutralize before adding water to your aquarium.
Fortunately, it is easy to make your tap water safe by using an aquarium water conditioner or dechlorinator. Simply measure out the right number of drops and add them to the water during your regular water changes. You probably don’t need to dechlorinate rainwater, well water, or reverse osmosis water, but a water conditioner is still useful to neutralize heavy metals.
pH
Water can be acidic, neutral, or alkaline and this important variation is expressed on a scale between 0 and 14. Water with a potential of hydrogen (pH) of 7 is neutral, and generally safe for most fish species. Water between 1 and 6 is acidic, and while some fish can live in a water pH level below 5, a value of 6 or more is safe for a much wider variety of species. Water above 7 is said to be alkaline, and some fish, like African cichlids, prefer alkaline water.
There are various ways to measure the pH of your water. Some aquarists use digital pH meters, but most fishkeepers use test strips or liquid test kits that change color.
It is possible to change the pH of your aquarium water by adding certain materials. Botanicals like Indian almond leaves can slightly lower pH while materials like crushed coral or oyster shells can raise it. However, it’s usually easier to keep fish that are naturally adapted to your water chemistry than to adjust your pH.
Water Hardness
Fish keepers are interested in two measures of water hardness, namely general hardness (GH) and carbonate hardness (KH). These important parameters are usually expressed in degrees or parts per million. Many strip test kits can measure water hardness, but you can also use liquid test kits to measure General H and KH.
General hardness describes the concentration of magnesium and calcium ions in the water. These minerals are important for your fish, although different bodies of water have different general hardness, and the fish that live there have evolved to thrive in that water chemistry. Many tropical fish, like tetras and danios, are at home in soft, mineral-poor waters with a low GH. However, some popular aquarium fish, like goldfish and African cichlids, prefer harder water.
Carbonate hardness is a measure of the carbonate and bicarbonate ions in water. KH is important because it helps to stabilize the pH in your aquarium. So, water with a low KH is more susceptible to drastic pH swings which can be dangerous for your fish.
