Surprisingly, a number of well-known freshwater aquarium plants will adapt to brackish waters. In general, species best suited for this prospect are those with waxy coverings on their stems and leaves. Many of the plant species that will survive in brackish aquariums are quite hardy in general. However, it is important to bear in mind that the change from a freshwater to a brackish water environment is extreme, and the plants should be given plenty of time to adjust. Increasing amounts of brackish water should be mixed into the water in which the plants are growing or should be allowed to drip in slowly through an airline tube.

Anacharis densa

A longtime favorite of freshwater aquarists and much used in grade school science experiments, this plant is perhaps the hardiest of the freshwater plants that may be acclimated to brackish environments. Under conditions of strong light, Anacharis can grow in height by more than 1 inch each day, and cuttings taken anywhere along the stem will result in new plants. It survives quite well as a floating plant or in rooted form.

Hornwort, Ceratophyllum demersum

Hornwort is an extremely common freshwater aquarium plant, various species of which grow worldwide. Most specimens are quite tolerant of both cold and fairly warm water. This large (to 10 feet, 3 meters) plant adjusts well to brackish water conditions but will pale in coloration if not provided with adequate lighting.

Vallisneria spp.

This well-known freshwater aquarium grass does very well in brackish water and seems to prefer subdued lighting. Unfortunately, the delicate leaves are much favored by herbivorous fish and invertebrates.

Water Sprite (Ceratopteris thalicroide)

Water sprite reproduces quite prodigiously and can overwhelm slower growing species even in the foreign environment of a brackish water aquarium. Water sprite is an ideal plant to begin with, as it can take on entirely different forms in the same aquarium. It survives quite well as a floating plant and, in this form, has rounded leaves. If rooted, the leaves that develop can be either thick and bulky or almost fernlike in appearance. Water sprite requires bright light and warm temperatures and is, unfortunately, much favored by plant eaters.

Chain Swordplant (Echinodorus tenellus)

Deriving the “chain” part of its name from its reproductive strategy of using long runners, this plant grows rapidly and matures at a height of 4 inches. In common with most sword plants, the chain sword requires warm waters and bright light.

Cabomba aquatica

This delicate beauty is very popular with freshwater aquarists. It is a tropical plant, originating in South America and is, unfortunately, quite delicate. It cannot survive the attentions of herbivorous animals and is easily destroyed by the activities of vigorous fish. In brackish water aquariums, it is best-kept with small, peaceable species such as halfbeaks or those that will not come in contact with it, such as mudskippers.

Sagittaria spp.

Sagittaria, a commonly kept grass, is one of the best freshwater species to use in brackish water aquariums. It is not prone to salt damage as are other freshwater plants, and aquarium animals tend to find it unpalatable.