Pro: Appearance

• A well-stocked aquarium complete with healthy green plants is aesthetically pleasing and makes your fish tank look fresh and natural. The stilted appearance of artificial plants is usually immediately noticeable, while having no plants can make the aquarium look sparse and uninviting. The appearance of your plants is an indication of the health of your aquarium: If there's something wrong with your water quality, plants will be the first to be affected -- a timely warning to do something before your fish get sick.
  
  

Pro: Biological Component

• During the day, live plants take in carbon dioxide and release oxygen. They have the ability to absorb toxins and harbor bacteria which help the fish. Floating plants that break the water surface discourage unsightly algae growth. In addition, plant matter provides food for most fish species.
  
  

Pro: Fish Concealment

• Depending on the mix of fish species in your tank, plants can provide invaluable hiding places. Female Siamese Fighting Fish, for instance, need somewhere to hide when the males become too sexually boisterous. Smaller fish can hide from larger ones intent on making a meal of them. For species such as the shy Plecostomus, plants allow it to remain unnoticed by more curious members of the aquatic community.
  
  

Con: Maintenance

• Looking after plants in an aquarium can be as time-consuming as tending to the fish. It's important to have some knowledge of them to ensure they're receiving the correct nutrients and amount of light. Leaves that decay need to be carefully removed, and fast-growing plants must be pruned. These are usually the floating varieties; when they grow too quickly, they suck nutrients and ammonium out of the water faster, which can be detrimental to the balance needed in the aquarium.
  
  

Con: Hidden Pests

• Introducing a new plant to your aquarium can have pitfalls: it could harbor unwelcome guests such as snails, hydras (tiny, predatory freshwater polyps), or fungal and bacterial diseases which could affect other established plants. Snails are particularly destructive as they breed prolifically and eat aquatic plants at an alarming speed. If a plant decays and isn't removed, it can encourage parasites; these may be harmful to the fish.