Learning about water chemistry is often avoided by most aquarium owners, but by knowing just the basics of water chemistry, you can greatly improve your success in rearing healthy fish.
Most aquarium owners are aware that the quality of water has a direct impact on the health of their fish. But many aquarium owners do not understand the basic internal chemistry of their fish's water, nor do they understand how to correctly or safely adjust it. Until the basics of water chemistry are mastered and some common water maintenance techniques are learned, it will be difficult to maintain a healthy and safe environment for the fish in your tank.
There are entire books written on the specifics of water chemistry, and I encourage all aquarium owners to learn as much as possible about this subject. The water quality is by far the single most important factor in the health of your fish, and the more you know, the better job you will do. This article provides a brief overview that is just the bare minimum that aquarium owners should know and understand.
pH
Every aquarium owner has heard of pH, but many do not understand the importance of controlling it. pH is the measure of acidity or alkalinity in the water. The pH scale is from 1 to 14. A pH of 7 is neutral, which basically means the water is not acid or alkaline. As the scale goes down, for example 6, the water becomes more acidic. As the pH goes up, for example 8, the water gets more alkaline. One very important part of the pH scale that most people do not understand is that it is a logarithmic scale. What this means is that the pH changes at a tenfold level between each number. For example, a pH 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. So if your fish are supposed to be at a pH of 7, and the water level is 8, they are in water that is 10 times more alkaline than what they should be. If the pH is 9, then they are in water that is 100 times more alkaline than what they need. So it is easy to see why even a small change in required pH is stressful and potentially fatal to fish.
These examples really emphasize the importance in matching your fish closely to the expected pH level of your water and then closely monitoring the pH. Putting a fish that requires a pH of 8 with a fish that requires a pH of 6 is just not a good idea because one or both will be at a very unacceptable level of pH and will be under a great deal of stress.
There are several different ways to influence your water's pH. There are chemical additives that can be added directly to the water that will either raise or lower the pH. More natural agents can be used to alter water pH as well. Peat in the tank or filter will acidify the water. Mineral salts like calcium that are found in limestone or in some shells will cause an increase in alkalinity and pH. There is one important consideration in altering the pH of water and that relates to the mineral content (hardness) of the water. See the section below for a complete description. Remember that fish are very sensitive to changes in pH, and rapid changes in pH can cause extreme stress and death. Fish should not be exposed to a change in pH greater than 0.3 in a 24-hour period.
Temperature
While not considered chemistry, water temperature needs to be mentioned. Fish are cold blooded, which means they cannot raise or lower their body temperature and their body temperature will be the same as the water around them. If a fish is kept outside of their normal temperature range they will become stressed and become diseased or die. The majority of fish are tropical, which means they come from temperate climates with water temperatures around 75°F. Even cold water species such as goldfish cannot handle very cold water or sudden changes in temperature. Know your species of fish and their temperature requirements.
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