No one can say exactly why fish get sick, but there are things you can do to prevent aquarium illnesses. Here are some tips to keeping your fish healthy.
Just as with people, fish often get sick when they become stressed. The two biggest factors that cause aquarium fish to be stressed are environment and nutrition. If the fish in your aquarium seem to continually become ill or even die, the following factors could be the cause.
If fish are not kept at the proper water temperature, or if there are sudden fluctuations in water temperature, the result is stress and sickness. This is especially true of the fish illness ich.
Pay attention to the exact temperature requirements of the fish in your aquarium. The proper temperature for tropical fish is 24ºC to 26ºC, but this could vary between species. For instance, clown loaches like water that is about 29ºC, so a tank kept at 24ºC would be too cold, would stress the fish, and make them more susceptible to ich.
Something else to watch out for in regards to temperature are rapid fluctuations. If the aquarium is near a heat register or air conditioner, the water temperature could go up and down rapidly throughout the day. This is especially true for aquariums that house goldfish, as many people do not keep heaters in goldfish tanks (but they should, for precisely this reason). Keep aquariums at least 1m away from any heating or cooling vents or devices.
There is often a correlation between water quality and fish becoming sick. The first step to checking the water quality is is to measure the ph value. The optimal value for many tropical fish is 7.0. Again, though, as with temperature, the ph value preferred by specific fish can vary greatly. For instance, angel fish like water that is slightly acidic, with a ph of 6.5, yet an African cichlid likes the ph around 8.2. Though both of these fish are from the same family, their ph requirements are vastly different. Make sure you know the preferred ph of the fish you plan to keep, as proper ph values prevent stress in fish.
You should also test for ammonia and nitrites in the aquarium as well. The presence of ammonia and nitrites in the water hinders the way the body of a fish works, thus negatively affecting their immune system.
Certain fish (like mollies, guppies, and puffers) like some salt in their water. Aquarium salt adds beneficial electrolytes to the water for the fish, improving their immune system. Yet other fish (platies, clown loaches) do not tolerate extra salt very well, and the addition of salt into their tank can stress them out, or even kill them.
Factors outside of the aquarium water can stress out fish as well. If the aquarium lights are left on day and night, this will affect the sleep cycles of fish (even if the fish are not diurnal, they still appreciate extended periods of darkness). Excess amounts of light will also cause algae in the tank to spread, which can also be detrimental to water quality.
Many times a television set or stereo speakers can stress out aquarium fish. Fish do not have the same perception of sound that we do, so the vibrations that a television or speaker sends through the aquarium can put the fish on edge. Keep aquariums away from the direct sound path of electronics. If the tank vibrates when the stereo is on, it is too close to the speakers.
You are what you eat and the same holds true for fish. Feeding fish a variety of different foods will keep them healthy. In addition to flakes, add some pellets or freeze-dried food into their diet. Frozen foods, like brine shrimp and bloodworms, are the closest prepared diets to what fish would eat in nature. Feeding your fish frozen food even once a week will greatly improve their health.
There are also supplements you can add to fish food to boost their immunity. Feeding fish garlic helps ward off parasitic infections. If chopping garlic into little tiny bits so that fish can eat them seems like too much work, a liquid supplement can be purchased from your local aquarium retailer. These supplements can be added to any food, but work best with frozen.
If you have predatory fish and buy feeder fish, make sure the feeders are healthy. Feeder fish with body fungus or ich can spread these diseases throughout the tank. Also, make sure the store where you buy your feeders feeds their feeder fish. If the feeders have sunken bellies and are starving themselves, they will not provide your fish with much nutrition. You should always feed your feeder fish before you feed them to something else.
How to Choose a Healthy Fish
Take a close look at the fish in the store before you buy them. If their fins are chewed up, they swim funny, have dull colors, or scratch their bodies against hard surfaces, choose a fish from a different tank. The last thing you need is to not only bring home a sick fish, but have that fish infect all the others in your aquarium. If the fish always look sick at a particular store (usually true of box stores), find a new place to purchase fish. A good deal on a fish isn’t a good deal if it dies 2 days later.
The best practice is to set up a small quarantine tank (an aquarium separate from the main one) and leave the new fish there for a week before putting it in the main aquarium.
Though a quarantine tank is ideal, it is impractical for many hobbyists. If an extra tank isn’t possible, at least feed the new an old fish very well, with frozen food, and maybe even a garlic supplement, when the new fish is introduced.