The aquarium is a small piece of nature in your home that provides opportunities for learning in biology, chemistry, math and ethics.
The fish in the tank, as well as any plants or any other living organism provide an excellent place to start teaching about biology. Discuss with your children what it takes to keep the fish alive. Food, oxygen and clean water are all necessary for the health of the fish. A lack of oxygen, over feeding or under feeding or putting dangerous (foreign) additives to the water can affect health of the fish. This can lead to a conversation about protecting our natural water sources and preventing pollution. If it can kill your aquarium fish, think about the impact on the natural environment.
If you have access to a microscope, it is also possible to watch the blood flow through a fish's fins (tail fin works best) but it must be done quickly to cause minimal stress to the fish.
All of the parameters of the water come into play when discussing chemistry. For example, you can learn what the pH of the water is, and why it is important for the particular fish you are keeping. The use of a basic fish book or online resource can help you know what the pH should be and explain why.
You can also look at the nitrogen cycle. When first setting up the tank, proper cycling allows the water chemicals to go from ammonia to nitrite to nitrate. You can easily test these chemicals with simple aquarium kits and only when the cycle is complete is it safe to put fish in the water. This cycling process can take up to a couple of weeks.
The water cycle is also evident in an aquarium as water evaporates out of the tank and needs to be replaced. Talk about why the water level dropped (evaporation) and where the water went. Tie the weather into the discussion with conversations on humidity. Also discuss how adding water to the fish tank is tantamount to rain in replacing the evaporated water.
When setting up an aquarium, you can use basic geometry to figure out how much water the aquarium will hold. 10 gallons of water looks very different in an aquarium than in 10 one-gallon milk jugs. Also, most medicines or water conditioners suggest x amount per y gallons and require simplealgebraic equations to figure out how much to add. Being able to perform these basic math skills may become more understandable and more enjoyable when applied to this real world use.
The aquarium can be a tool for teaching ethics as well. It is important to teach children to properly care for and handle animals and to give them the respect that they deserve. Aquariums provide an excellent opportunity for this discussion and also can lead into deeper discussions, such as when it is best to put down a fish. One note of caution - flushing a sick fish is extremely cruel. The chemicals will strip the protective slime coating on the fish and in essence the fish will burn to death.
Having an aquarium in your home is not simply a relaxing part of your home decor, but can serve as an excellent learning tool as well!