Death in the Fish Tank - A Whatdunnit Quiz

Answer: Poison - insufficient bacteria to break down fish waste

Any brand new tank and filter system needs time to establish a colony of bacteria to break down the nitrogenous waste of the fish (which is deadly to them when it builds up). You should leave your newly-filled tank fish-less for the first three days, then start with only one or two fish of a hardy species to cope with the initial toxic load.

The right kind of bacteria is already present in the water, and will soon start a colony. You can then add one or two new fish each week. Commercial bacteria can also be purchased to help kick-start a colony, or a handful of gravel from an established tank can be added.

It is recommended to use test kits for ammonia, nitrite, and nitrate to gauge the water quality when starting a new tank. Even when established, a tank needs partial water changes to keep nitrate levels low.

Answer: A sudden change in temperature or pH

Sudden changes in temperature or pH (acid-alkaline balance) can kill fish. Any bag containing new fish should be floated in your tank for at least fifteen minutes to allow the temperature of the two environments to equalize. Also, you should tip some of your tank water into the bag to reduce the shock of any changes in pH or water quality.

It is also a good idea to transfer the fish from bag to tank with a net, rather than tip the water in, because pathogens may be present in the water of another tank.

Another tip when adding new (and therefore stressed) fish is to avoid feeding them for the first day.

Answer: A lack of oxygen in the water

Fish need free oxygen molecules in water for respiration, and this oxygen comes from the mixing of air with water. In nature this occurs through running streams, waterfalls, and ocean waves. In aquariums it is accomplished simply by creating ripples on the surface from the flowing water which returns from the filter pump, or by using bubble-blowing devices.

Answer: Dr. Whatson's sponge

It's elementary - soaps and detergents are fish-killers. Soap destroys the lining of the gills of fish, making respiration difficult or impossible. Always clean your tank and its objects without soaps or detergents. As for tobacco smoke, the general recommendation is that it's best to avoid exposing your fish to it, but in practice it rarely seems to cause problems.

It is quite likely to kill you, however.

Answer: Male Siamese fighting fish will actually kill each other

"Should I buy four fighting fish, or only one? Well, should I, Punk?" Male Siamese fighting fish (also called bettas) are always kept in separate tanks in stores for a good reason - they instinctively kill each other on sight! Keeping incompatible fish is a common cause of "fishicide" in aquariums.

Many members of the cichlid family, for example, do not mix well with other fish. Also, as a general rule, big fish will eat little fish. Research is important when choosing your fish.

Answer: The pH was too acidic

For nitrate levels, up to 20 ppm (parts per million) is generally safe. For temperature, most tropical fish prefer something in the range of 25-30 degrees Celsius. For pH (acid level), however, a safe level is usually close to neutral (7.0), and outside a range of 6.0 to 8.0 can be toxic. Each species will have something of a pH preference, but 4.1 would typically be fatally acidic. Be aware also that rapid fluctuations in pH can be more harmful than the level itself, so if using a commercial pH balancing agent, be careful to follow the directions in order to make gradual changes. Always use a pH testing kit to confirm the level of acidity.

Answer: Chlorine in the water

Chlorine in public water supplies can kill not only your fish but also the beneficial bacteria in your tank. Always use a water-conditioning agent (water ager) to instantly convert chlorine to less harmful compounds, ideally in a plastic tub before adding it to your tank. Because of potential changes in pH, water hardness, etc, it is also advisable to replace no more than 50 percent of your tank water in one day. How much and how often you replace tank water depends on the size, type, and number of fish and plants you have, but 20 percent once a week, or 40 percent every two weeks, is a good rule of thumb.

Answer: Paint and solvent fumes contaminated the water

Fumes from oil-based paint, solvents or insecticides can kill many species of fish. It is best to temporarily seal the tank with a non-porous material like plastic sheeting and turn off any filters and air-compressors for the duration. For larger renovations or procedures which create heavy fumes, it may be best to temporarily relocate the fish or the tank itself.

As for noise, fish can actually tolerate quite a bit of it. What they don't like are flashes of movement or bumps to the tank.

Answer: An icky disease called "Ich"

Ichthyophthiriasis, also known as white spot disease, or simply "Ich", is a common parasitic disease which appears as little white specks, singly, or in groups on the body or fins of freshwater fish. It can cause irritation and make the fish breathe rapidly, lose appetite, or rub against objects.

In severe cases it will cause death. Depending on the type of fish affected, treatment involves the introduction of salt, raising tank temperature, or the use of commercial preparations. Fish with Ich should be isolated from non-infected fish.

When purchasing fish, it is important to check them for any visible signs of disease, erratic behaviour, or lack of vitality.

Answer: Clownfish require saltwater

Remember the movie "Finding Nemo"? Nemo was a reef-dwelling clownfish. A saltwater tank is needed for such marine creatures. Always find out what kind of environment fish require when (or preferably before) purchasing them. Some fish need a specific water quality, some do best with plants, rocks, shade, lower pH, or a certain diet.

Some vendors may assume that a customer already knows these things.