Water lettuce are floating plants there require a LOT of very high lighting, therefore they should only be in outdoor ponds. In a home aquariums, they usually do not get enough light to grow healthy, not to mention they block the plants below from getting enough light. They have thick root masses that rot if the plants are dying from insufficient light. Water lettuce is even harder to keep healthy than water hyacinth as the leaves that are below are shielded by the leaves above and they tend to 'melt' due to lack of light, leading to water pollution. This plant is better left alone.