Water Lettuce

The Lid Condensation Death:

The 'Wet Leaf' Rot. Like many specialized floating plants, Water Lettuce leaves are covered in millions of microscopic water-repellent (hydrophobic) hairs designed to keep the top of the leaf bone dry. THE FATAL FLAW: It is strictly designed for 'Open-Top' rimless aquariums or outdoor ponds. If you put it in a traditional aquarium with a tight glass or plastic lid, the intense humidity and condensation will drip heavily from the lid straight onto the top of the fuzzy leaves. This constant top-down soaking destroys their air-breathing pores. The leaves will rapidly turn yellow, then into a disgusting black mush, and rot away completely. You MUST ensure good ventilation above them.

Root Trimming and Nutrient Greed:

The Root Forest. Because they pull massive amounts of fertilizer (Nitrates, Phosphates) directly from the water, their roots will grow insanely long. If the roots hit the sand or tangle up your fish, you can literally just take scissors and give the plant a brutal 'haircut', chopping off 80% of the root length. The plant is incredibly resilient and will just regrow them. If the beautiful green leaves suddenly turn intensely pale or yellow, it means they have greedily sucked the tank entirely dry of Nitrates and are starving.