Basic Water Chemistry

What is water chemistry?

Many beginning aquarium owners dread learning about water chemistry. But just by knowing the basics, you can greatly improve your track record in rearing healthy fish. Since water quality has a direct impact on the health of your fish, it's important for aquarium owners to understand basic water chemistry in order to adjust it correctly and safely. Aquarium owners who learn the basics of water chemistry find it much easier to maintain a healthy and safe environment for aquarium fish.

Of course, there are entire books written on the specifics of water chemistry - we encourage all aquarium owners to learn as much as possible about this subject. This article series provides only a brief overview of water chemistry basics, beginning with "hard" vs. "soft" water: how dissolved minerals affect the quality of your aquarium environment.

Water Hardness

Does hard water have a high pH or low pH?

Water Hardness & pH Levels

Water hardness is often confusing and therefore overlooked by many aquarium owners, though quite important because it is closely related to pH levels. Many fish can only thrive in certain levels of water hardness, and if the levels are outside acceptable parameters, it can cause stress and death. Also, until you get the right water hardness or softness in your aquarium, you won't be able to effectively moderate the pH levels crucial to healthy and happy aquatic life. There are water conditioners to assist hobbyists in adjusting different mineral levels in the home aquarium.

Water hardness can be most simply described as the mineral levels in the water. Hard water has a high dissolved mineral content. Soft water has very little. The most common mineral in water is calcium; however, other minerals may also be present. Tap water is either slightly hard or soft depending on where it originates. Well water from areas with a lot of limestone (calcium) is often hard. Water that comes from lakes and rainwater is often devoid of minerals, making it soft.

It is important to understand how water hardness affects pH in your aquarium. Hard water (high mineral content) is usually high in pH. Soft water (low mineral) is typically low in pH. The mineral in hard water acts as a buffer that combats aridification in the water. The resulting water will be more alkaline and higher in pH. Some species of fish require hard water while others require soft water.

How do you turn hard water into soft water?

Without the Correct Water Hardness, You Can't Fix pH Levels

The problem arises when we try to lower the pH in hard water. If we add a commercial pH decreaser to an aquarium with hard water, the mineral in the hard water will buffer the water and make it difficult to successfully lower the pH. We first have to remove the mineral from the water before we can effectively lower the pH. To soften hard water, you need to take the mineral out with a water softener or use demineralized water for your fish tank.

How do you turn soft water into hard water?

The same is true for trying to raise the pH in acidic water that is soft and has a low mineral content. Until we add minerals to the water, it will be difficult to successfully alter and maintain a high pH level. So, what do we do? The easiest step to take is to add minerals in the form of calcium-based rock, thus making soft water hard and more alkaline (higher in pH).

Is it okay to put fish in hard water?

Of course, the alternative to all of this may be to tailor your fish and plant species around your existing water source. For the beginning aquarist this may be the best solution. There is a wide variety of tropical fish available and at least a dozen different species suited best for every different type of water. Quality providers like LiveAquaria® will list the individual pH and hardness requirements of different species of fish.

The pH Scale & Your Aquarium

Many beginning aquarium owners dread learning about water chemistry. But just by knowing the basics, you can improve your success in rearing healthy fish. Since water quality has a direct impact on the health of your fish, it's important for aquarium owners to understand basic water chemistry in order to adjust it correctly and safely. Aquarium owners who learn the basics of water chemistry find it much easier to maintain a healthy and safe environment for aquarium fish.

What does pH measure?

Many aquarists have heard of pH, but most do not understand the importance of maintaining stable pH levels in their aquarium. The pH measurement you get when testing shows the level of acidity or alkalinity in water, recorded in a range from 1 to 14. A level of 7 is considered neutral, the point at which water is neither acidic nor alkaline. As the numbers decrease from 7, the water’s acidity is increasing. As the pH range increases from 7, alkalinity is increasing.

One particularly important thing to know about the pH scale is that it is logarithmic. For example, a pH level of 5 is 10 times more acidic than a pH of 6, and a pH of 4 is 100 times more acidic than a pH of 6.

Can fish with different pH level requirements share the same tank?

If your fish thrives in a pH of 7 but the water in your aquarium measures 8, your water is 10 times more alkaline than what it should be. If the pH is 9, then your fish are living in water 100 times more alkaline than recommended for optimal health. Knowing this, it is easy to see why even a slight change in required pH can be stressful - and potentially fatal - for your fish.

Expecting a fish that requires a pH of 8 to share the same water with a fish that requires a pH of 6 is not sensible because one or both will always be under a great deal of stress. These examples emphasize the importance of matching your fish closely to the expected pH level of your water and then closely monitoring the pH.

How can I change pH levels?

There are several different ways to influence your water's pH. There are chemical additives you can add directly to the water which will either raise or lower the pH. Natural agents can also be used to alter water pH as well. Adding peat in the tank or filter will acidify the water. Mineral salts like calcium (found in limestone or in some shells) will increase the alkalinity and pH.

Any time you attempt to change pH levels in your aquarium, remember that fish are extremely sensitive to pH changes and if it's done too rapidly, it can cause extreme stress or even death. Fish should not be exposed to a change in pH greater than 0.3 in a 24-hour period.

Ammonia, Nitrites and Nitrates

What do you know about water chemistry?

Many new aquarium owners dread learning about water chemistry. But by becoming familiar with the basics, you can greatly improve your track record in rearing healthy fish. Since the quality of aquarium water has a direct impact on the health of your fish, it's important for aquarium owners to understand the basics of aquarium water chemistry in order to adjust it correctly and safely. Aquarium owners who learn the basics of water chemistry find it much easier to maintain a healthy and safe environment for aquarium fish.

How does ammonia become nitrate?

Break it Down: Ammonia, Nitrites, and Nitrates

Ammonia, nitrites, and nitrates are all byproducts of organic waste breaking down in an aquarium, and all are toxic at some level to your fish and plant life. A significant amount of fish and plant waste can accumulate in any aquarium (as well as uneaten food, algae, and bacteria). As in all environments, this waste needs to be broken down and either eliminated or turned into something that can be utilized by another organism. In an aquarium, there is a population of bacteria that is responsible for this process. The breakdown of nitrogenous waste is a four-part process:

What is the process of converting ammonia to nitrates?

1. First, the waste from fish, plants, and food breaks down and releases ammonia.
2. This ammonia is very toxic to fish and is converted to nitrite by nitrifying bacteria.
3. Nitrite is also toxic to fish and is converted to nitrate once again by beneficial nitrifying bacteria.
4. Nitrate is not as toxic and is used by plants or algae to help them grow.

Because high levels of ammonia and nitrite are lethal for fish, it is critical that these products be efficiently removed or converted to nitrate. Nitrate, nitrite, and ammonia can also be removed through weekly water changes.

Do I need a biological filter for an aquarium?

The Importance of Biological Filtration

Maintaining a population of bacteria that convert ammonia into nitrite is an important part of aquarium water chemistry; a process known as biological filtration. Biological filtration will occur naturally in most aquariums that have been up and running for a couple of months. New aquarium filters often contain a special area or wheel made specifically for providing an optimal habitat for growing these bacteria.

While the bacteria will live in a traditional filter and on rocks in the aquarium, these new biological filters can harbor a much larger colony and can, therefore, do a better job of removing ammonia and nitrites.

If an aquarium is overcrowded, or waste levels get too high through overfeeding, even a properly functioning biological filter can be overwhelmed, resulting in cloudy aquarium water and eventually toxic conditions. Periodically checking the ammonia and nitrite levels in your aquarium with a test kit will ensure that your biological filter is working efficiently.

A healthy population of aquatic plants will also aid in the removal of nitrates. Because it takes months for an aquarium to establish a healthy population of beneficial nitrifying bacteria, it is important an aquarium establish itself before adding fish. After several weeks with only a few hardy fish, more fish can be slowly added over the next couple of months to make sure the biological filter isn't overloaded.