Some foods, although nontoxic to your fish, will not provide adequate nourishment and will leave them susceptible to disease and parasites. Other foods are rich sources of nourishment, but require additional preparation and handling before being fed to fish. Still others are perfectly fine but only in moderation.

Human vitamin supplements should not be administered to your fish. Human supplements do not benefit your fish and may cause harm.

Freshwater fish food, such as goldfish food, should not be given to saltwater fish. The fatty acids in freshwater animals and marine animals differ. Over time, your fish will develop a fatty acid deficiency that will stunt its growth, leaving it susceptible to disease and shorten its life.

Avoid giving floating foods to saltwater fish. Few saltwater fish are surface feeders, resulting in uneaten food.

Finally, never feed beef heart, liver or other meats to your saltwater fish. The fish will not benefit from meat because the proteins are different from those in their natural diet.

Do not feed saltwater fish food such as frozen smelts or prawns to your freshwater fish. The fatty acids in freshwater animals and marine animals differ. Over time, your fish will develop a fatty acid deficiency that will stunt its growth, leaving it susceptible to disease and shorten its life.

Live foods will need special handling before feeding, including housing. Also, freshly caught, live food can introduce parasites into your tank.

Many worms, particularly tubifex worms and earthworms can carry debris, organic material and bacteria that can infect your tank. They must be washed very well before being fed to your fish. Some experts refuse to use tubifex worms, despite their high nutritional content, because of the diseases they can carry. If you choose to feed your fish tubifex worms, a good alternative to live worms is feeding freeze-dried worms, as that process removes a lot of the harmful bacteria that can be present.

Make sure all live foods are healthy.

All fish food should be used in moderate quantities. Fish need a varied diet to ensure they receive all the nutrients they require. Leftover food will rot and reduce the water quality in the tank. If you find you have accidentally fed too much food, wait until the fish have finished eating, then use an aquarium vacuum or a siphon to remove the excess food.

If you feed tubifex worms, you should know that those not eaten will immediately burrow into the gravel at the bottom of the tank where they will die and pollute the water. Because of this, feed these worms in very small quantities at a time, if at all.

Make sure you buy aquatic plants from a reputable dealer and check to make sure what you are buying is really an underwater plant. Remove all dead or dying plants from your tank as soon as possible because decomposing plant matter will harm the water quality in your aquarium.

A floating aquatic plant that can be more of a pest than a danger is duckweed. This plant can rapidly cover the entire surface of an aquarium, which can negatively affect your fish by limiting the amount of light that enters the aquarium. The best solution to this problemis to not include duckweed in your tank at all. If you do decide to have duckweed, make sure to prune it often.

Enthusiastic landscapers with saltwater tanks may want to add driftwood to the tank, while those with freshwater tanks may want to add bogwood, wood that has been soaking in lakes and streams for several years. However, newly fallen branches may contain resins and other compounds that can be harmful to your tank. Pine branches are particularly dangerous. Also, the wood may be home to a number of live organisms you do not want to add to your tank. It is safest to buy wood that is specifically for aquarium use. Follow the manufacturer instructions for treating it before adding it to your tank.