Plants

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 illuminated 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.

Breeding

Some brackish water fishes can be bred in the aquarium. The easiest fishes are the livebearers like guppies and mollies, closely followed by the hardy cichlids like kribensis. These species will breed even in community tanks, and provided the young aren’t eaten, you will soon have a problem finding homes for your new fish!

Where breeding can be obtained easily, brief notes are included in each species entry for the interested; but as a rule most aquarium books cover these species. Baensch’s Aquarium Atlas is probably the best European reference book for many unfamiliar species. TFH also publish numerous fish breeding books. A useful primer to fish breeding is Fish Breeding by Chris Andrews, part of the ‘Interpet Guide To...’ series.

On the other hand, many brackish water fishes have not been regularly spawned in captivity. Fishes such as Monodactylus sebae have been bred only on a very occasional basis while the breeding habits of others, like archerfish, are completely unknown. In many cases this is probably because the fishes are large and up till now insufficient tank space and number of individuals have been kept. As aquaria become easier to manage and people keep larger tanks, hopefully this problem will be overcome. Even so, some ‘triggering factor’ may be lacking, such as changes in salinity or temperature. With such fishes there is plenty of scope for experimentation.

If you want to breed aquarium fishes, perhaps the most reliable species to begin with are:

• Kribensis -- egg layer, guards spawn and fry; fry easy to feed
• Orange chromides -- egg layer, guards spawn and fry; fry need small live foods
• Bumblebee gobies -- egg layer, guards spawn and fry; fry need small live foods
• Mollies -- livebearers, fry big and easy to feed
• Halfbeaks -- livebearers, pregnant females somewhat delicate, but fry easy to raise

It is almost always best to keep fishes you want to breed in a separate tank with the minimum of decoration. Try to keep the tank as clean as possible, and remove any uneaten food. Use a good filter, but make sure the flow isn’t so strong it would suck up eggs or the baby fishes (fry). Provide nesting sites for those fishes that need one, such as a small flower pot turned on its side (ideal for gobies and dwarf cichlids). Feed the parents on the best food you can; frozen bloodworms and crustaceans are ideal conditioning foods and will complement a good quality flake food nicely. In the case of livebearers, remove the male after the female has become pregnant. Generally female livebearers will ignore their offspring after they have been born. Cichlids can be left together as pairs if they are coexisting, although if one or other of the parents is not behaving well it can be taken back to the community tank. Be aware that in the case of many cichlids the first or second broods are not always successfully raised. Sometimes the parents eat the eggs or fry. Don’t worry -- they eventually get it right! Male gobies are often in sole charge of the brood, in which case the female can be removed if she is being attacked. In all cases it is important to give the fishes, particularly the females, a rest between breeding cycles.

Healthcare & Medication

As mentioned in the introduction, one of the best low-technology ways to keep brackish water healthy is to vary the salinity. While these fishes are well adapted to fluctuations, many common external parasites are not. Simply exposing freshwater whitespot to full strength seawater will kill it and all its spores. The reverse is true for marine pathogens: expose them to freshwater and they will die. The simplest option is to remove the infected fish and dip it into a bucket of fresh- or saltwater as required. If several fishes are infected, then an option for an aquarium with hardy brackish water species like scats or monos, it is simple enough to change the salinity of the aquarium for a few days. Make the change gradually, over a few hours, and keep an eye on nitrite levels. The filter bacteria should be okay, but as a precaution remove some of the filter media before making the salinity changes. This reserved media can be put back into the filter if something goes wrong, with the salinity returned to its original level of course. Not all brackish water fishes will tolerate big changes in salinity (e.g. rainbowfish, spiny eels); see the lists of species below for details.

Commercially available remedies can be used in brackish water aquaria. In lightly salted water (1.005 or less) freshwater branded chemicals can be used, but in general marine chemicals are better. Never use freshwater remedies if you are keeping invertebrates, since these frequently contain copper which will kill many molluscs and crustaceans.

Water Temperature & Chemistry

Most tropical brackish water fish will do at temperatures of 20 to 25° C (68 to 77° F). A few species appreciate slightly warmer conditions, for example archerfish and bumblebee gobies prefer the temperature to be not less than 25° C (77° F). When using an aquarium heater, ensure that you are using one that is safe in salt water -- some are not.

Fishes from the temperate zones will not do well at tropical temperatures for long. While many species will adapt to ambient room temperature provided the oxygenation of the water is adequate, other species may require a chiller, particularly in summer. Aim for a temperature of around 15° C (59° F) and certainly no higher than 18° C (65° F).

Fish from slightly brackish water (such as kribensis and spiny eels) are generally not picky about pH or hardness provided extremes are avoided. A slightly acidic to neutral pH with low to moderate hardness appears to suit these fish best. Species from the more marine end of the spectrum, such as monos and scats, need hard, alkaline water conditions. Sea salt contains minerals that should harden the water and make it more alkaline, but at low salinities sea salt alone may not be adequate. A good way to ensure a high pH and hardness is to use calcaereous media in the filter, such as coral sand or crushed coral.

Using these as a substrate for an undergravel filter does work, but over time bacteria and algae coat the grains reducing their effectiveness. It is more reliable to place the calcareous media in a canister filter where it can be more easily removed, cleaned, or replaced.

Sea shells will also help to buffer the water. Do not use snail shells from the garden, garden pond, or anywhere else that you cannot be sure the shells have not been exposed to poisons such as insecticides and herbicides. Shells from the fishmongers or grocery store (such as oysters, scallops, and clams) can be used but clean thoroughly beforehand. Small quantities of meat are often left in the shell even after the shellfish has been prepared for eating, and these will decay in the aquarium. Small fish such as gobies are especially fond of shells and will use them as resting places and spawning sites.

Do not use dead corals in brackish water aquaria. Besides not being a natural part of brackish water ecosystems, many corals are threatened by over-collecting (among other pressures) and there are perfectly adquate artifical alternatives.

Bogwood can be used in brackish water aquaria, but it does tend to acidify the water. In tanks containing hard water this effect will be minimal, but the tannins released by the wood will still tint the water yellow or brown. This is not intrinsically bad, and some fish, such as glassfish, look especially nice in slightly coloured water.

Salinity & Specific Gravity

I have written a computer program called Brack Calc that convert between salinity, specific gravity, and salt concentration. You can download Macintosh and Windows versions of this program here.

Sea salt is more than just sodium chloride, it also contains calcium carbonate and bicarbonate, various metal salts, and small amounts of phosphates, sulphates and nitrates. For this reason adding table (cooking) salt is not an adequate substitute. Neither are the aquarium tonic salts sold for community tanks. The best way to make brackish water is to use proper seasalt (marine mix) sold for reef aquaria.

If you have a marine aquarium, good quality water from the marine aquarium can be used in the brackish water aquarium. To make half-strength seawater for example, you would mix old marine aquarium water with fresh tap water in equal amounts. Always remember to add dechlorinator. The ‘old’ water from the marine aquarium needs to be of reasonably high quality, so check the nitrate level to make sure that it is not excessively high. Nitrate levels up to 50 mg/l will be tolerated by most brackish water fish without complaint.

Salinity is a measurement of how much salt is dissolved in the water. It is difficult to measure, so most aquarists prefer to describe the saltiness of the water as a density. The density of a substance is how heavy (how much mass it has) per unit of volume. Pure water has a density of 1.000, i.e. one litre of water weighs one kilogramme. Seawater is denser as it has salt dissolved in it. Typically seawater has a density of around 1.025, which means one litre of seawater weighs 1.025 kilo grammes.

Hydrometers and refractometers

To measure the density of the water you will need a hydrometer, a device that measures the density of a liquid. Most hydrometers sold for aquarists are calibrated to be accurate at around 20 to 25° C. Swing arm hydrometers are commonest. These are small plastic devices, which are filled with the water to be measured. In doing so an arm moves inside the device which points at a scale, from which the density can be read. Cheaper, but less often seen, are floating hydrometers. These look a bit like glass thermometers with a weight at the base and a scale running up the glass. These are also sold with brewer’s kits for people who make wine and beer. So long as the scale runs from 1.000 to 1.030 or so then they are fine. Floating hydrometers are placed in the tank or bucket of water to be tested and left for a moment. When the device settles, the surface of the water will cover the scale up to the density which can be read off.

The density of water required varies depending on the fishes kept. Fishes from the fresher end of the range (like rainbowfish and kribensis) enjoy a density of less than 1.005, as do most freshwater plants. Fishes which live mostly in from the sea, like dog face puffers and batfishes, prefer a salinity of over 1.010. But most brackish water fishes can tolerate the entire range: from 1.000 to 1.025. These include such fish as sailfin and black mollies, sleeper gobies, monos, scats, archerfish, and shark catfishes.

If you can’t get a floating hydrometer which shows the entire range the alternative is to use a swing arm hydrometer and dilute full strength seawater. For example, if you want one-tenth seawater, or about 1.002 to 1.003, you would make full strength (1.025) seawater and then dilute it with freshwater in the ratio one part salt to nine parts fresh. One half seawater, about 1.012, would be made by mixing one part salt water to one part fresh.

What about the hand-held refractometers now widely sold online for around $50? On paper at least, these appear to be more accurate than hydrometers. In practise though, consumer-grade refractometers are not comparable with lab instruments. A hand-held scientific-grade refractometer would cost aroudn $1000, and desktop instruments even more. Are the cheaper, consumer-grade refractometers even useful? Yes, they work at least as well as good quality hydrometers. Both refractometers and hydrometers will only be accurate if maintained and used correctly. But it is far from clear that refractometers are actually better than hydrometers, as this discussion over a Reef Central illustrates.

Can you measure out the salt in teaspoons or tablespoons?

Measurements like one teaspoon per litre are sometimes mentioned. One teaspoon of salt weighs about 6 grammes, so very roughly, you can estimate the amount of salt using teaspoons. Water at SG 1.005 for example contains 9 grammes of salt per litre, so for a 10 litre bucket, you’d add 90 grammes of salt, or 90/6 = 15 teaspoons.

Making up your water

However you measure your salt, it is important never to add the salt directly to the aquarium. Not all the salts dissolve at the same rate, and some can damage your fish when undissolved. Always make the salt water up separately, following the instructions on the package carefully. Allow the salts to fully dissolve, there should be no residue at the bottom of the container. Stirring helps, but best of all use an airstone to bubble the water for twenty minutes or so.

Salt water is highly corrosive. Most metals corrode quickly even when splashed by salt water. It is therefore important to make sure that no metal objects are used inside the aquarium, and metal hoods and stands should be avoided.

Substrate

The most natural substrate is sand, but this is not ideal for use with an undergravel filter. If you have an undergravel filter, a shallow layer of sand (less than 2 to 3 cm) can be placed on top of regular coarse gravel. The sand will need to be separated from the gravel using a gravel tidy, a sheet of mesh which will keep the two layers mixing. The sand will be give burrowing fish like flounders and eels something to root about it, without interfering with the correct function of the gravel as part of the filtration system.

Plain beach sand can be used, but typically it is rich in lime and consequently hardens the water. For those brackish water fishes used to more marine conditions this isn’t a problem, but those fishes that come from the slightly brackish, more neutral conditions higher up the estuary, too high a pH and hardness can be undesirable. Moreover, few aquarium plants do well in lime-rich sands. Unless sold specifically for aquaria or horticulture beach sand is often rather dirty and so does need to be cleaned well before use.

Silica (or silver) sand is a better choice because it is chemically inert, and so won’t affect water quality or act as a buffer. But because it is inert it will not take up chemicals used in the aquarium, including medicines, and then leach them back out. Silica sand is rarely sold in aquarist stores, but is inexpensive and widely sold in garden centres and horticultural outlets where it is particularly marketed for use with cacti and certain other house plants. Mixed with fine (pea) gravel and laterite, silica sand forms an excellent substrate for most aquarium plants. Because this mixture packs down with time, it becomes slightly anoxic, which many plants appreciate because this condition favours the release of minerals like iron that they need to grow. However, this combination cannot be used with an undergravel filter, but an undergravel or undertank heater works well to circulate water within the substrate. Also, unless a there is good plant growth with an extensive network of roots throughout the substrate, fine sands can become dangerous anoxic, harbouring anaerobic bacteria capable of producing a gas, hydrogen sulphide, that is toxic to fish. In tanks with few plants or none at all, the sand should be stirred on a regular basis and any organic matter siphoned away during a water change. To be fair, burrowing fish should quickly root out any live worms or bits of food that get hidden in the sand (catfish and spiny eels are both very good in this regard) but it is best not to take any chances and clean the sand thoroughly at least once a month and be very sure not to let it become too deep or compacted in any part of the aquarium. The depth of sand in an unplanted tank need only be enough for the fish to burrow into comfortably, something like 2-6 cm being adequate for flounders and spiny eels.

Course calcareous sands, such as coral sand, make good undergravel filter beds, either in the tank or in an external canister filter and have been widely used by marine aquarists in this way. As a substrate they are quite light reflective, which tends to make fishes ‘wash out’ their colours. For this reason it is not ideal. As with beach sand, freshwater plant growth is not reliable in coral sand. Marine algae, like Caulerpa , do very well in it.

Standard non-calcareous gravels are the most widely used substrates. As a general rule, for plants the finer the better. Fishes kept alone need only enough to cover the bottom (1-2 cm). For big non-burrowing fishes, like Monodactylus and gar, a good effect can be gained by mixing a medium to coarse grade gravels with water worn pebbles and a few boulders. Such a substrate is easy to clean and will not trap pieces of food. It also allows plenty of swimming space and avoids sharp edges that the fish might scratch themselves on. Burrowing fishes should be given only smooth, fine gravel, or sand of some sort, as mentioned above.