Watersprite

Among the fastest-growing aquarium plants, watersprite can double its mass in under two weeks under moderate light. Ceratopteris thalictroides is a pantropical fern with finely divided light green leaves that can be grown rooted in the substrate or left floating at the surface — one of the few plants that works both ways without changing its leaf form.

It produces proliferous leaves: tiny plantlets form along the parent leaf midrib, each ready to grow into a new fern once detached. This makes it effortless to propagate and useful as a fast-growing nitrate sink during tank cycling or in overstocked aquariums. When floating, the hanging roots provide cover for fry and shrimp.

CO₂ injection is not necessary. Without it the leaves stay finer and more delicate; with supplementation they grow larger and more robust. The plant tolerates a wide pH range from soft acidic to moderately hard water. The main caution is that its rapid growth can shade out slower plants below, so regular thinning is needed in a mixed planted tank.