Large organic water lettuces (4 for $2)

Safe for fishes and shrimps. No chemical. No pesticides or growth enhancers. No tap water. 

In addition to providing hiding places and microorganisms (as food) for fishes, water lettuce aggressively consumes decomposition byproducts in water, such as nitrate, nitrite, and phosphates, as well as other organics. It is a very effective plant for keeping your aquarium waters in chemical balance and healthy for fish and invertebrate life.

As with many surface-dwelling, buoyant aquatic plants, they can restrict light penetration to deeper levels of the aquarium stifling the growth of algae and also sequester the nutrients necessary for algal growth. Water lettuce is very effective at controlling algae levels in an aquarium environment.