Tropical Community Tanks
1. Tank quite new, but lots of fish are
Almost certainly down to poor water quality. The
biological filter takes about four to six
weeks to mature. While you can speed this up in various ways, it
is still easy to overstock/overfeed and end up with poor water
Use an ammonia or nitrite test kit to check water quality. Do lots of water changes; this will dilute the nitrite and ammonia,
helping the fish to recover.
2. Tank is mature, but lots of fish
There are three likely causes: poor water quality,
rapid changes in water chemistry, or the accidental poisoning of the
water. It is relatively rare for a killer disease to suddenly spring out of nowhere, though if you recently
introduced some new fish, they can certainly have brought diseases
with them (which is why you should quarantine new livestock).
Use an ammonia or nitrite test kit to check water quality. Are you are feeding the fish? Is
filtration is adequate? Is the tank
overstocked? Are you doing enough water changes? Most community fish are adaptable in terms of
water chemistry, but use a pH test kit to ensure water chemistry stays stable. If necessary, incorporate
chemical buffers to maintain pH. Possible
poisons include pesticides, paint fumes, and other such
Small tanks (37
litres/10 gallons or less) are difficult to maintain and easily
overstocked. Water quality and water chemistry will fluctuate
quickly in these systems, stressing your livestock. If you have a
small tank, upgrading to one above 70 litres/20 gallons in size will
dramatically improve your hobby (as well as the lives of your fish).
3. Some of my fish are sick
The vast majority of times fish get sick, the disease
involved is whitespot, velvet, finrot, fungus, or the shimmies. Use
this article to establish which disease is causing your
problems, and then select the appropriate treatment.
Note that most of the WWM crew aren't wild about tea tree oil products such as
Melafix and Pimafix. At best these are unreliable cures, at worst
completely useless. There are ample, medically-tested products out
there: use those instead.
4. Livebearers (Mollies, Guppies, etc.)
All Central American livebearers need hard, basic water. If kept in soft, acidic
conditions they are prone to diseases such as finrot.
Mollies are additionally very sensitive to nitrate, particularly
if kept in freshwater rather than brackish or marine conditions.
Mollies are therefore most easily maintained (and some would say
only ever reliably maintained) in brackish water with at least 3-6
grammes of marine salt mix per litre (SG 1.003-1.005). Because
Mollies, and to some degree livebearers generally, have very
particular water chemistry requirements, they are best maintained in
their own aquarium rather than a standard community system.
5. Neons dying one at a time; everything
else is the tank is fine
Neon tetras are prone to a disease known as
Pleistophora hyphessobryconis or Neon
Tetra Disease (NTD). The symptoms start with shyness and loss of
appetite, the infected neon usually leaving the school and hiding in
a dark corner. Gradually the colours fade to off-white, the fish
becomes lethargic, either bloated or emaciated, and then dies.
There's no cure. The best you can
do is isolate infected fish to prevent infection of healthy fish.
Observe the fish carefully, and if the symptoms match NTD,
painlessly destroy the fish. Pleistophora can infect species
other than neons, though infrequently.
Neons can of course become sick because of other
things such as finrot and fungus, so simply because you have a sick
neon, don't automatically assume it's Neon Tetra Disease.
6. Dwarf Gouramis are becoming emaciated,
losing their colour
Dwarf gouramis are prone to a virus known as the Dwarf Gourami Iridovirus. One study by vets found that 22% of
the dwarf gouramis exported from Singapore were infected with the
virus. Infected fish gradually weaken and lose their colour,
eventually developing sores and lesions on the body. The faeces
become stringy and pale. The virus appears to be 100% fatal and completely incurable; it is also highly infectious.
Sick fish should be isolated at once, and if Dwarf Gourami Disease
is confirmed by careful observation of the symptoms, the fish should
be painlessly destroyed.
Dwarf Gouramis may become sick for a variety of other
reasons, and diseases like finrot and fungus can create
superficially similar symptoms. That said, the quality of dwarf
gouramis on the market is very variable,
so take great care when shopping for these fish. Ideally avoid them
altogether and opt for hardier, easier to maintain species such as
Colisa fasciata and Colisa labiosus.
7. Fin-nipping, or some of your fish have
Ragged fins can be a symptom of finrot, but if your aquarium enjoys good water quality
and the fish seem to have had bites taken out of their fin
membranes, fin-nipping may be a problem. Multiple so-called
community tank species are known to be fin-nippers and should never
be kept with slow-moving or long-finned species (such as angelfish
and guppies). Among the most common fin-nipping fish are various
(though not all)
Hyphessobrycon spp. (most notoriously serpae tetras and jewel
tetras); Gymnocorymbus ternetzi (also known as petticoat
tetras, black tetras, and black widows); and Puntius tetrazona (also known as tiger
8. Snails everywhere!
Snails turn uneaten food
and other wastes into baby snails. If you have problems with snails,
then the first step in fixing things is to establish what they're
eating. Avoid using snail-killing potions: having lots of dead
snails rotting in your aquarium will reduce water quality
dramatically. There aren't any completely community-tank safe fish
that eat snails, though loaches and thorny catfish (family
Doradidae) will eat snails if they are sufficiently hungry. But do
be aware that loaches are gregarious and often boisterous fish, and
thorny catfish will also eat very small fish including neons.