Top five points:

1.       Neons must be kept in schools of six or more specimens in at least 37 litres/10 gallons.

2.       Neons will not live long in hard, alkaline water.

3.       Neons must not be kept too warm; 22-24 C/72-75 F.

4.       Neons need a dark, shady, preferably well planted aquarium.

5.       Neons will be eaten by larger fish, including Angelfish.

Introduction

Neon Tetras (Paracheirodon innesi) are very popular fish, with millions of them imported into the US alone. But despite their low price and wide availability, they aren't the easiest fish to maintain. Beginners often find it difficult to keep Neons alive for more than a few months. The reasons for this are varied, but problems with water chemistry and water temperature are certainly part of the problem, as well as the widespread incidence of Neon Tetra Disease among farmed Neons.

Description and Taxonomy

Neon Tetras are small, minnow-like fish from tropical South America. They are transparent except for an electric blue band running along the upper half of the body from the eye to the adipose fin and a red band beneath the blue band that runs from the abdomen onto the base of the tail. During the night these colours are 'switched off', and this can cause some alarm when aquarists confuse this normal action with the loss of colour seen when Neons get sick. Sexual dimorphism is minimal, though females in breeding condition will be noticeably plumper because of the eggs they are carrying. Adult length is about 3-4 cm/1.2-1.6 inches.

Neons belong to a small group of tetras, Paracheirodon, that includes two very similar species, the Cardinal Tetra (Paracheirodon axelrodi) and the Green Neon Tetra (Paracheirodon simulans). Both the Neon and the Cardinal have names that honour aquarists: William Innes in the case of the Neon, and Herbert Axelrod in the case of the Cardinal.

Habitat

Neon Tetras come from shallow, sluggish streams deep within the rainforests of Brazil, Colombia and Peru. The water in these streams is very soft and acidic. Because these streams are in shade and thick with rotting vegetation, the water is cool, gloomy, and stained brown with tannins and humic acids. In fact Neons have their brilliant colours so that they can see each other in the gloom. The lack of light also means that aquatic plants aren't a major part of this habitat, and instead Neons live in streams thick with tree roots, decaying wood and leaf litter.

Aquarium maintenance: tank size, Filtration and Decor

Neons are not especially active fish, but because they need to be kept in groups of at least six specimens, their aquarium should be at least 37 litres/10 US gallons in size. That will not only provide ample swimming space for 6-10 specimens, it will also leave enough space for suitable tankmates, of which more will be said later.

Neons dislike strong water currents. Air-powered filters are ideal, and sponge, box, and undergravel filters all suit them very well (though undergravel filters cannot be used in combination with sand). If you must use an electric canister filter, whether internal or external, or a hang-on-the-back filter, choose a model that provides a relatively low turnover rate, 4 times the volume of the tank per hour being about right. In other words, for a 10 US gallon aquarium, choose a filter rated at about 40 US gallons/hour.

If you want your Neons to show their best colours, their aquarium should be as dark as possible. In other words, avoid bright light and don't use unnatural substrates that reflect light upwards from the bottom of the tank. Neons may be kept in a planted aquarium, where they will usually stay close to the bottom where the vegetation is thickest. Alternatively, you could create a more realistic setting using bogwood roots, smooth sand and Indian almond leaves to recreate leaf litter. Blackwater extract or peat granulate can be used to tint the water, but be aware that this will lower the pH over time and cuts out the light that plants need, though shade-tolerant epiphytic plants like Java moss, Java fern and Anubias spp won't mind too much.

Black sand is a good decorative material for the Neon tank, but it tends to be too sharp to use in tanks with bottom-feeding fish such as catfish. Smooth silica sand, also known as silver sand and pool filter sand, is a safer alternative. Despite its yellow-tan colour, this sort of sand is very similar to the silica sand found in many South American rivers and streams, so fits in with the biotope.

Bogwood is an authentic addition to the Neon aquarium and when either placed on the bottom to resemble sunken wood or else planted vertically to simulate tree roots. Bogwood will acidify water over time, so take care to monitor pH if carbonate hardness is much below 5 degrees KH. Otherwise artificial bogwood roots can be used just as effectively but without any risk of water chemistry changes.

Water chemistry

Although Neons come from soft and often very acidic streams in the wild, they are fairly adaptable in terms of water chemistry. Anything between 2-10 degrees dH, pH 6-7.5 will suit them well. They may accept slightly harder and more alkaline conditions, up to perhaps 15 degrees dH, pH 7.5, but not always.

Note that domestic water softeners do not create soft water in the sense that is meant here, because all they do is replace temporary hardness (carbonate hardness) with sodium salts so that limescale problems are minimised.

If you live in a hard water area, then mixing your drinking water with reverse-osmosis (RO) water or rainwater should create conditions that suit your Neons. For example, 'liquid rock' hard water of the sort that comes out of chalk aquifers commonly has a general hardness around 20 degrees dH and a pH around 8; when mixed 50/50 with RO water or rainwater the resulting water chemistry should be around 10 degree dH, pH 7.5, easily good enough for Neons as well as most other South American tetras and catfish. If you live in a hard water area and do not have access to RO water or rainwater, then Neons are not a good choice for your aquarium.

Do not confuse pH with hardness! Simply adding a pH buffer to hard water will not create soft water conditions, and the resulting unstable water chemistry conditions will likely stress your fish.

Water temperature

Neons do not like excessively warm water; between 22-25 degrees C/72-77 F is ideal. Short periods of warmer water during summer will do them no harm, but if continually maintained above 25 C/77 F they will not do well. Likewise, colder conditions will stress Neons, making them much more likely to sicken and die.

Diet

In the wild Neons feed mostly on insect larvae and tiny crustaceans, but they are very adaptable in aquaria and readily take flake and small pellet foods. Occasional offerings of live brine shrimp and daphnia are worthwhile though, if only to provide the indigestible material that helps to avoid bloating and constipation. Neons rarely take food from the surface but instead snap at food that is drifting through the bottom half of the tank.

Social behaviour and Tankmates

Neons are intensely social fish that must be kept in groups of at least six specimens. Indeed, one of the best indicators that a Neon is sick will be its failure to school properly alongside its tankmates. The bigger the group, the happier your Neons will be, and it's well worth keeping them in groups of a dozen or more specimens for best results. Some stores give discounts when fish of the same species are bought in large groups.

Good tankmates for Neons will be species similar in size and temperament that share the same need for cool, soft, slightly acidic water conditions. Among the South American tetras and characins that get along well with Neons are Red Phantom Tetras (Hyphessobrycon sweglesi), Black Phantom Tetras (Hyphessobrycon megalopterus), X-Ray Tetras (Pristella maxillaris), Marbled Hatchetfish (Carnegiella strigata) and Golden Pencilfish (Nannostomus beckfordi). Virtually all the Corydoras catfish work well with Neons, though the dwarf species like Corydoras hastatus and Corydoras habrosus would be the best choices for tanks smaller than 60 litres/15 US gallons. Among the South American suckermouth catfish, Otocinclus spp. work well, as do Bristlenose Catfish (Ancistrus spp.) and Whiptails (Rineloricaria spp.). Dwarf cichlids tend to bully Neons, but the acaras are generally peaceful enough to ignore Neons most of the time, in particular the Keyhole Cichlid (Cleithracara maronii), the Flag Acara (Laetacara curviceps) and the Red-breasted Acara (Laetacara dorsigera).

If you want to look outside South America for potential tankmates, possible choices include Cherry Barbs (Puntius titteya), Dwarf Golden Barbs (Puntius gelius) and Five-Banded Barbs (Puntius pentazona). The bigger barbs like Tiger Barbs and Ruby Barbs are too aggressive to work well with Neons and are best avoided. Danios such as Zebra Danios (Danio rerio) and Pearl Danios (Danio albolineatus) are an option, but danios are pushy, hyperactive fish likely to hog any food that doesn't quickly sink down to the lower levels where Neons prefer to feed.

Among the fish to avoid are species that need hard, alkaline water including the Central American livebearers like Guppies, Mollies, Platies and Swordtails. Species that need warmer water than Neons should also be avoided, perhaps most notably the Gouramis. While Neons are not normally nippy fish, there are numerous reports of them pecking at the fins of Siamese Fighting Fish, so that's another combination to avoid.

Neons are small fish and many opportunistic predators will view them as potential meals given the chance. Angelfish are notorious Neon-eaters, despite the common combination of Neons and Angels seen in aquarium book photographs. Other occasional Neon-eaters include Spiny Eels (Macrognathus spp.), Giant Danios (Devario aequipinnatus) and Pimelodus Catfish (Pimelodus pictus).

Healthcare

Neons are quite hardy fish when given the right environmental conditions. Many problems come from trying to keep them in hard or excessively warm water, as well as the usual problems associated with poor water quality and overstocking, as well as mortality caused by bullying and predation.

However, one particular problem does need to be mentioned: Neon Tetra Disease. There is some debate among aquarists about which Neons have 'true' Neon Tetra Disease as caused by Pleistophora hyphessobryconis as opposed to 'false' Neon Tetra Disease caused by an opportunistic bacterial infection. Casual aquarists will probably find this academic, since telling the two apart is impossible outside a microbiology lab. 'False' Neon Tetra Disease has been treated with antibiotics with occasional success, but 'true' Neon Tetra Disease is untreatable and invariably fatal.

Neon Tetra Disease usually becomes evident when one of the Neons leaves the group and instead hides away by itself, often at the back of the tank. Indeed, it is often the case that the aquarist realises something is wrong because his or her school of Neons appears to be one short. Over time affected Neons stop eating as they become weaker, and they usually lose their colour as well, the blue band in particular become much fainter than usual. Death occurs within a few days of these symptoms becoming evident.

As stated earlier, 'true' Neon Tetra Disease is invariably fatal, but it is also highly contagious, so any Neons exhibiting these symptoms should be removed immediately. Treating with antibiotics in a hospital tank may be worthwhile just in case the aquarist is dealing with 'false' Neon Tetra Disease, but otherwise affected Neons should be humanely destroyed. Immersion in a mixture of 30 drops of clove oil in 1 litre/4 cups of aquarium water will kill a Neon Tetra within a few minutes and without undue stress or pain.

Neon Tetra Disease is transmitted through tissue fluids, most often when healthy fish cannibalise the corpse of a dead Neon. This is why removal of sickly fish is so important.

Breeding

Neons are egg-scatterers and are considered to be quite easy to breed and details will be found in most books about breeding fish. Successful breeding depends upon proper conditioning first, which means keeping mature adults in optimal conditions and feeding them three or four times per day on small portions of suitable live foods such as daphnia. The water should be between 1-2 degrees dH in general hardness and should have a pH between 5.5 and 6. Water temperature should be about 22 C/72 F.

Once the females are ripe with eggs and noticeably plumper than usual, pairs can be moved to a spawning tank around 30 litres/8 US gallons in size. Provide gentle filtration and stock the tank with feathery plants like Cabomba and Myriophyllum, but do not use any sort of aquarium light. Instead allow morning sunshine to strike the tank for a few hours, and raise the temperature to about 25 C/77 F.

Males drive the females through the plants where a few dozen eggs per spawning session. The adults can then be removed and the tank kept as dark as possible (light seems to stop the eggs from developing properly). The fry emerge after 24 hours, and after another 3-4 days are ready to feed on tiny live foods including infusoria. Some success has been had using liquid fry foods as well. A week later the fry are ready to move onto brine shrimp nauplii and/or finely powdered flake food.

Neon fry grow quickly, but as with fish fry generally, they are sensitive to old, stale water so it is important to provide regular water changes to keep conditions in the rearing tank nice and fresh.

Artificial varieties: Long-fin, Diamond, Gold and Albino Neons

Long-Fin Neons have been bred to have longer fins than normal Neons. Obviously they cannot be kept with nippy tankmates, but it is also important to use a smooth substrate and gentle filtration so that the fins don't get torn. Even under the best circumstances they tend to end up looking ragged. Crooked spines are often seen among Long-Fin Neons, suggesting they may be rather inbred.

The Diamond Neon is a new variety that has blue spots on its head instead of the usual blue stripe along the flanks. Otherwise it conforms to the standard Neon in terms of care, and unlike Long-Fin Neons doesn't seem to suffer from any particular health problems.

The Gold Neon has a yellowy rather than silver body, and the red and blue stripes on its flanks are far weaker than on normal Neon Tetras. This variety isn't especially attractive and doesn't seem to be widely sold. The same holds true for the Albino Neon, a form that has an even paler body than the Gold Neon as well as the pink eyes typical of albino fish. It is even more sensitive to bright light than ordinary Neons, and perhaps a touch more delicate in terms of overall care.

The Other Paracheirodon: Cardinals And Green Neons

Cardinals look like larger, chunkier versions of Neons with a more extensive red band that runs the full length of the body. Basic care is identical to that of Neons, except that Cardinals need warmer water, ideally 26-28 C/79-82 F. As such they're an excellent choice for community tanks maintained at higher than average temperatures, and work well with Lace Gouramis, Ram Cichlids, Angelfish and Discus. Cardinals get to an adult length of 4-5 cm/1.8-2 inches.

If kept in soft, acidic water conditions Cardinals are quite hardy. Only occasionally do they suffer from Neon Tetra Disease, usually when they've been kept alongside farmed Neons. Most of the Cardinals traded are wild-caught and quite expensive, typically 2-3 times the price of farmed Neons, but less expensive farmed Cardinals are increasingly widely sold.

Green Neons are still pretty rare in the trade. They resemble ordinary Neons but have a greenish rather than transparent body; they also tend to be smaller too, about 2.5 cm/1 inch in length when fully grown. Care is almost identical to that of the Cardinal Tetra, but they are shyer and absolutely must be kept in a quiet aquarium with suitably warm, soft, and acidic water conditions. They are not good community fish, except with small, peaceful tankmates: Pencilfish, Kuhli Loaches, Whiptail Catfish, Sparkling Gouramis and so on.

Close: Some Hard Water Alternatives To Neons

As wonderful as Neon Tetras can be, aquarists dealing with hard, alkaline water conditions would do well to skip Neons in favour of fish likelier to do better over the long term. X-Ray Tetras in particular are easy to keep and adaptable, and will tolerate hard water much better than Neons, even water as hard as 20 degrees dH posing them no particular problems. X-Ray Tetras are very peaceful fish, and make excellent community tank residents. The Red-Eye Tetra (Moenkhausia sanctaefilomenae) is another very sturdy South American tetra that will thrive in hard water, but it is boisterous can will sometimes nip at the fins of slow-moving tankmates such as Guppies and Angelfish, so it's best kept with reasonably sturdy companions like catfish, loaches, danios and so on. X-Ray Tetras can do well in tanks as small as 60 litres/15 US gallons, but Red-Eye Tetras are that bit more active and will need a tank at least twice that size to do well.

A school of Celebes Rainbowfish (Marosatherina ladigesi) could make a fine alternative to Neon Tetras. At up to 8 cm/3 inches in length they're a bit bigger than the Neon, but they do have some of the electric blue colouration that makes Neons so eye-catching, this time as a blue stripe halfway along the flank towards the base of the tail. Otherwise they are basically transparent except for various black and yellow markings on their fins. Celebes Rainbowfish are playful fish that do best in well-planted aquaria with plenty of swimming space; keep them in long tanks at least 75 litres/20 US gallons in size. Dwarf Rainbowfish (Melanotaenia praecox) are another good alternative to the Neon Tetra. These are deep-bodied metallic blue fish with red to purple fins, and while not an exact substitute for the Neon, they are hardy and easy to keep, and as such one of the best small schooling fish species for hard water communities.