Water lettuce is compatible with most fish, although larger fish like cichlids may damage it. However, it should be completely avoided in any tank containing goldfish or any other large herbivore fish, as they tend to eat the roots, and even the plant itself.Click to see full answer. Besides, is water lettuce toxic to fish?Water lettuce is an aggressive surface grower, which can kill fish by depleting oxygen. The leaves contain poisonous calcium oxalate crystals, which can cause illness when ingested or chewed, especially by small animals and children.One may also ask, is water lettuce an oxygenator? Water hyacinth, water lettuce, and duckweed are all members of the floating plant group. Submersed plants are the best oxygenators, as they release oxygen (O2) directly into pond water. Correspondingly, what does water lettuce do? Water lettuce is grown for its foliage, but it does bloom. The insignificant flowers are usually hidden down between the leaves. Being a floating plant, water lettuce obtains all it?s nutrients directly from the water. This makes it a great plant to use to combat algae.How do you keep water lettuce alive? Care of Water Lettuce In warm climates, the plant will overwinter or you can grow water lettuce indoors in an aquatic environment in a mix of moist loam and sand with water temps between 66-72 F. (19-22 C.). Additional care of water lettuce is minimal, as the plant has no serious pest or disease issues.