Planting a brackish water aqurium is not easy because only a limited range of truly brackish water tolerant plants are widely traded, but on the other hand some regular freshwater plants can adapt to lightly salted water.
In general plants need strong lighting on for twelve hours a day (any more tends to promote algae) and a substrate rich in laterite. The minimum lighting for good plant growth is two fluorescent lights equal in length to the aquarium. Tanks deeper than 45 cm (18 inches) will not be illumina
ted adequately with ordinary lights and will need more powerful halogen or mercury vapour lamps. Undergravel filters should not be used with plants because they interfere with the chemistry of mineral absorbtion by the roots. Obviously plants that don’t have their roots in the sediment, such as floating or epiphytic plants, are not affected in this way by undergravel filters.
The following are plants that I or other brackish water aquarists have found to work well. A useful reference for aquarium plants is the website of the commercial plant grower Tropica.
Salt-tolerant freshwater plants (trace amounts of salt, 1.000-1.003)
Anubias barteri is an epiphytic plant that is usually sold encrusting bogwood or stones. It has attractive dark green leaves. Sometimes it is sold in pots where it does okay, but not as well as if tied to a piece of bogwood with cotton and allowed to grow normally. Anubias is a slow-growing plant but is tolerant of a range of conditions including low levels of light. It is also sturdy enough to do well with even quite large, active fish. Anubias is propagated by cleanly cutting the encrusting stem into pieces and attaching these portions to new pieces of wood as needed.
The hornwort Ceratophyllum demersum is a fast growing plant that can be used rooted in the sediment or more easily as a floating plant. It is brittle and apparently considered tasty by vegetarian species of fish, and so should only be used with small non-herbivorous species. Ceratophyllum demands a great deal of light and regular feedings of iron and other nutrients otherwise the leaves turn pale and eventually die. This plant propagates itself vegetatively by forming small, floating daughter plants.
Indian Fern Ceratopteris thalictroides is a good choice for tanks with livebearers and halfbeaks. It provides shade and shelter, and the roots and leaves of this floating species make excellent hiding places for newborn fry.
The so-called moss ball Cladophora aegagropila is a freshwater alga that does well at low salinities, and makes an unusual and generally quite hardy addition to a community tank without algae-eating species.
Crinum thaianum, or onion plant, is so named on account of the bulb from which the long strap-like leaves grow. It is slow growing but fairly hardy, and can be used as more durable and long-lived alternative to Vallisneria. This plant needs a deep, laterite enriched sediment and strong lighting.
Cryptocoryne wendtii is a hardy, but rather sombre looking plant that will grow slowly but reliably even with low light levels. It does need a rich substrate though. Periodically daughter plants form at the end of runners that can be removed and planted elsewhere. Various hybrid Crypts are sold in many aquarium shops, and often these do well in slightly brackish conditions too.
Hygrophila polysperma and Hygrophila corymbosa (“Nomaphila stricta”) are fast growing, somewhat woody or at least stiff stemmed species with variable leaves arranged in rosettes up the entire stem. When doing well these are sturdy and attractive plants but they need a rich sediment, preferably with laterite, and certainly strong lighting.These plants are apt to become etiolated or ’leggy’ in poorly illuminated tanks, with the plant being mostly stem with only small, pale green leaves near the very top. They also need regular feedings of iron or else the leaves become chloritic, or abnormally pale. Propagation is by cuttings, which if placed in the sediment should take root.
Vallisneria spp. are medium-to large, strap-leaved plants with leaves that get to 60-200 cm in length depending on the species. In general terms they are extremely easily to maintain. Their main requirement is for moderately bright to bright light and a substrate reasonably rich in nutrients (plain gravel with fertiliser tablets works fine). Given good conditions their growth is extremely rapid and they will quickly spread out across the aquarium via daughter plants that appear on the ends of runners. Always plant Vallisneria with only their roots, and never the white/green ‘crowns’, in the substrate. Old leaves should be broken away at the base.
Freshwater plants that naturally occur in slightly brackish water (1.000-1.005)
Bacopa monnieri is a medium sized plant with green stalks and small round leaves. It needs very strong lighting and frequent feedings of an iron rich fertliser to do well. Bacopa monnieri is a somewhat fragile plant that can be easily damaged by boisterous fish. Propagation is by cuttings, which if placed in the sediment will develop roots.
Crinum calamistratum and Crinum pedunculatum have long leaves growing from a bulb. They grow more slowly thanCrinum thaianum (see above) but are more reliable in salty water. Otherwise kept in the same way.
Cryptocoryne ciliata is one of the few species in its genus that regularly occurs in brackish water, although it does demand quite strong lighting and rich substrate to do well.
Lilaeopsis brasiliensis is a grass-like plant that although slow growing will eventually form a dense ‘turf’. It needs a lot of light and a good rich sediment.
Microsorium pteropus or Java fern is an epiphytic fern that is usually sold attached to pieces of bogwood. Large plants, known as ’mother plants’, are particularly impressive and bushy. Do not plant Java fern in the sediment, it will rot and die. The Java fern is popular with aquarists because it is adapable to low light conditions and tolerant of soft, hard and even slightly brackish water. There are many varieties of Java fern available but all seem to share the same basic needs. Although reputed to be toxic and generally ignored by most fish, Baensch reports scats eating this plant and then dying.
The Java moss Vesicularia dubayana is one of the best brackish-tolerant species for small tanks and is particularly noted for its tolerance of relatively low light levels. Growth is rather slow, but generally steady. Rather few fish eat this plant, but it can be damaged by boisterous species.
Freshwater plants that naturally occur in strongly brackish water (1.000-1.012)
Samolus valerandi is a marsh plant common in brackish as well as freshwater habitats. It has a very high tolerance of brackish water; accordingly to Frank Schaefer in the Aqualog brackish water fishes book, tolerating salinities up to 30 ppt, around SG 1.020 at 25 degrees C. However, Samolus valerandi is a difficult plant to grow. It needs a rich substrate and strong lighting.
Mangroves & Sea Grasses
Note: See also Anthony Calfo’s article on mangroves at WetWebMedia, here.
Mangroves are common brackish and salt water tolerant trees found all around the tropics. The roots and stems are underwater while the branches and leaves are above the water. They will not grow permanently submerged. Mangrove trees form a classic brackish water habitat known as a mangrove forest or mangal, around the roots of which swim many species of fish familiar to the aquarist, including archer fish, monos and batfish. Juvenile sharks, tarpon, groupers and other normally offshore fish species can be found here as wel.
Aquarium Fish Magazine volume 7, number 15 (1995) has a detailed article on keeping mangroves in aquaria. Mangroves need strong light, plenty of space and a deep substrate to do well. Various websites advertise mangrove plants, for exampleMangrove.at, and you can sometimes find them offered for sale in marine aquarium stores. But the key thing is to obtain either pods without leaves (which adapt well to any salinity) or more mature plants adapted to the salinity of your system. For some reason, once the pods have developed leaves and roots, they don’t always tolerate being moved from one salinity to another.
Sea grasses (also called turtle grasses) are not algae but true flowering plants with well developed root systems and proper flowers that use water instead of wind or insects for pollination. In appearance they resemble Vallisneria quite closely. Sea grass ‘meadows’ are a distinctive marine habitat favoured by many invertebrates particularly snails and shrimps, as well as fishes like flounders, seahorses and pipefish. Sea turtles and in particular manatees and dugongs feed extensively on sea grasses. Although widespread and locally very common, sea grasses are very rarely offered for sale to aquarists although collecting native species may be possible (subject to local regulations of course). Sea grasses tend to be inhabitants of fully marine environments rather than brackish ones, although several species are found in estuaries. It is important to check which species you have before using it in a brackish water aquarium.
Marine Algae
Although there are many naturally occuring brackish water algae none are commercially traded. Nondescript algae will likely develop in a brackish water aquarium anyway, but if you want to grow larger, more decorative species, the addition of algae collected from brackish water habitats will almost certainly be necessary.
The otherwise hardy and adaptable Caulerpa spp. do not tolerate reduced salinity well. The invasive form of Caulerpa taxifolia for example dies at or below 20 ppt, around SG 1.014 at 25 degrees C.
