|MadSci Network: Botany|
Yes indeed Emily, you have algae in your tank. This is a very common occurrence in fish tanks and is a problem for many fish-keepers. The algae don't usually harm the fish, but it sure makes the tank look nasty. You may not even be able to see the fish inside.
Many algae live as only one, single cell. Almost all algae live in or near water, fresh or salty. There are a few types that live in the soil. There are also algae that combine with fungi to make lichen. The fungus keeps the algae protested from drying and gives some nutrients. The algae give back to the fungus because it can gather energy from the sun. This is important because lichens don't live in easy places. Lichen is the blue-green or gray smudges you see growing on tree trunks and rocks. These are tough places to live for simple creatures.
Some algae are not quite so simple. Some look much more like land plants. These are the seaweeds. But they, too, must live in water because they are missing one thing that land plants have -- a way of moving water through their bodies. So they stay in the water so they don't have to move it around.
Fish tanks are just wonderful places for algae to grow. They are usually nice and warm and fish waste makes great algae food. (It makes good plant food, too. Try using the water you take out when you do a water change to water your potted plants. They will love it!) The other thing that algae (and plants) need to grow is light. Your tank is probably in a nice bright spot so you can see the colors of your fish. You may even have added some nice aquarium lights to show off the fish better. Well, you just about made the perfect home for algae.
So you have a nice cycle. Your fish (and you and me and all animals) use oxygen and give off carbon dioxide when they breathe. You add fish food, which the fish eat. Then the fish produce waste that contains nitrogen, an important chemical in plant food. So you have oxygen and fish food going into the fish and carbon dioxide and nitrogen coming out.
Now, the algae are pretty much the opposite. They use carbon dioxide and give off oxygen and they use the nitrogen in fish waste with light and carbon dioxide to grow. So here you have carbon dioxide and nitrogen going into the algae and oxygen going out.
You can draw a picture with fish on one side and algae on the other. Use arrows to show what goes in and what goes out of the fish and algae. Does it look like a circle? This is recycling the natural way!
There are many scientists who study algae and some great ones are in Australia. Look them up at the Universities. If you want more information about algae, there are several good websites.
These have links to many algae sites:
Also, Pictures of diatoms (the glass walled algae): http://www.indiana.edu/~diatom/diatom.html
and Seaweeds: http://seaweed.ucg.ie/seaweed.html
Try the links in the MadSci Library for more information on Botany.