Aquatic plants literally liven up the look of an aquarium. They give fish a place to hide and help convert carbon dioxide into oxygen, improving water quality. But adding plants to a tank can prove dangerous to the health of your fish if you don't take the right precautions.
Fungus and Disease
Plants can carry disease, fungus and bacteria; infected ones will bring unwanted organisms with them into a new aquarium. Even when they come from a trusted source, you need to disinfect live plants to remove anything that could be dangerous for your fish before you add them to your tank. To disinfect an aquatic plant without killing it, soak it in potassium permanganate for 10 minutes and rinse it with conditioned aquarium water.
Snails
A snail or two in your aquarium can be cute. When those few turn into a handful, it's entertaining; but when the snail population suddenly explodes, it's a problem. You can have them even if you don't introduce them purposely: They smuggle themselves into your tank by laying eggs on plants. If you put the plants in the tank without removing the eggs, you could wind up with a tank full of the sluglike creatures. Kill the eggs prior to anchoring by placing the plants in an alum bath for two days. The bath should be composed of 1 to 2 tablespoons of alum per gallon of water.
Algae
Algae will make its way to your aquarium whether or not you include plants, but adding plants that already have algae on them can overwhelm your tank. If you notice algae on the plants you intend to introduce, dip them in a bleach solution for about two minutes and rinse them with treated aquarium water. The bleach solution should contain 1 part bleach to 20 parts water.
Quarantine
If you have the space, quarantine your new plants in a separate tank for at least three weeks. In combination with disinfecting, this ensures that any disease organisms in the plants die before they have a chance to infect the fish. The organisms perish during the quarantine period due to the lack of a host, making the plants safe for your fish.
Water Conditions
Even healthy plants that aren't carrying any disease, fungus, bacteria, snails or algae can wreak havoc on your tank if you aren't careful. Plants change water chemistry, usually in a positive way by taking in carbon dioxide and releasing oxygen; but any sudden change can be stressful for your fish. Add a few plants at a time, let the water adjust for a few days, then add a few more. This will keep your aquatic ecosystem from getting overwhelmed by the changes new plants cause.