Fungus is present in all healthy freshwater and saltwater environments, including aquariums. Too much or certain kinds of fungus, however, can create problems for aquarium plants and fish.
What Is Fungus?
Fungi are in a kingdom all their own and are not considered to be either plants or animals. They are natural decomposers--breaking down organic matter and replenishing nutrients back into the soil or the water. Although most are not harmful to plants or animals, some types can cause illness or even death.
Fungus In Aquariums
Fungus thrives in moist environments rich in organic matter. Aquariums, especially those with an abundance of fish and live plants, are a natural breeding ground. This is particularly the case with aquariums that are not properly cleaned or contain sick or dead fish.
If you don't clean and properly use water treatments, you might see black fungus growing on your fresh water aquarium plants. This type of fungus won't hurt your fish, but it can kill your plants and will continue to spread unless you treat it by adding salt-reducing treatments to your water because this fungus is attracted to high levels of salt.
If you see white fungus growing on your aquarium plants, you should remove the infected plants immediately. This type of fungus can be very harmful and even fatal to your fish. It can quickly spread to the mucus membranes and other sensitive areas of a fish, so it is important to treat your water and your fish as soon as possible. Ask your local pet store to recommend the best treatment based on the types of plants and fish in your aquarium.
Algae are considered to be a type of fungus because they are neither plants or animals. Every aquarium contains algae, and small quantities are beneficial. If allowed to grow and spread, however, algae can compete with your aquarium plants for valuable nutrients and sunlight and can eventually cause them to die. The most common types of aquarium algae are green algae, red algae, blue green algae and diatoms. Algae can be removed physically, with the use of algicides, and by introducing catfish and sucker fish into your tank.