Cleveland Aquarium Society

Aquarium disease prevention

As the saying goes, "an ounce of prevention is worth a pound of cure" and these wise words are never so true as they are when applied to fishkeeping. Medicating a large aquarium can be a major hassle, especially if you have live plants, invertebrates, scaleless fish, or valuable/rare specimens to take into consideration. However, if you follow these relatively simple preventative measures, you should never have to medicate your display tank.

Regular Maintenance

Consistently excellent water quality can do much to prevent disease and to minimize the damage that an outbreak can cause. I recommend that you perform a twenty to fifty percent water change every week or, at minimum, every other week, as part of your regular maintenance routine. Neglecting water changes can lead to a high concentration of nitrates and plummeting pH levels, which will stress your fish and make them more susceptible to disease. Also, if you have been slacking on your water changes, the chemistry of your tap water will become quite different from that of your tank, so when you finally decide to clean the aquarium, a too-large water change could shock your fish.

Be sure to check all of your equipment regularly. A malfunctioning heater could "cook" your fish if it gets stuck in the "on" position, while a sudden chill could weaken your livestock's immune systems, making them susceptible to a myriad of diseases.

Appropriate Temperature

Warm-blooded animals (like humans) have bodies that are able to produce enough heat to keep their systems functioning properly, regardless of the exterior temperature (within limits, of course). Cold-blooded critters (like fish) depend on the temperature of their environment to keep their metabolisms, immune systems, and other physical processes in proper working order.

A sudden change of temperature can kill a fish instantly (if it is extreme) or cause an outbreak of disease due to stress on a weakened immune system. For instance, a sudden drop in temperature is often followed by a bout of "ick" (a common opportunistic parasite). Fish that are consistently maintained at too-low temperatures will have slower metabolisms, weaker immune systems, and be less active than they would if kept in a proper environment. They may not die instantly, as they may if exposed to sudden changes, but they will probably be sicklier and die much younger than they would have otherwise.

This is typically why most experienced hobbyists don't recommend adding a plecostomus or other "cleaner" fish to a goldfish tank. Goldfish prefer the cooler temperatures of an unheated tank while the ubiquitous plecos are better suited to a more tropical environment. A tank that is well-suited to one of these fish will be very uncomfortable for the other, so it is best to house them separately.

Proper Diet

I suggest purchasing several different types of food and rotating them. Most community tanks should receive a regular flake or pellet, a vegetable-based food, and some type of frozen food or live food (brine shrimp, black worms, blood worms, plankton, etc). Many would also benefit from fresh vegetables, such as romaine lettuce, blanched zucchini, or peas.

The only fish that should regularly receive live feeder fish are those that absolutely refuse to eat anything else. And even these fish should never be given goldfish or rosy red minnows. Both of these common feeders are high in fat, low in nutrition, and often carry diseases that your fish may contract. A steady diet of goldfish can lead to fatty deposits around your fish's organs, malnutrition and related diseases (such as hole-in-head), poor water quality (feeders are very messy), and disease outbreaks caused by pathogens that the feeders carry.

If you have a gar or another fish that is difficult to wean onto prepared food, I recommend raising your own feeders. Livebearing fish (such as guppies and platies) are easy to raise if you need smaller food. Convict cichlids, are as prolific as many rodents and produce copious numbers of offspring that may serve as larger feeders. Raising your own feeder fish ensures that they are free of disease and nourishing for your display fish.

Oscars, piranha, and most common aquarium fish are easily weaned onto prepared foods and happily eat pellets, krill, and frozen silversides. These are cheaper, more convenient, cleaner, and healthier than a diet of goldfish.

Quarantine New Fish

I can't tell you how many times I've heard people blame a store for selling a sick fish that infected their entire tank. This always upsets me because the fault lies with the hobbyist, not the store! You should always examine the fish you wish to purchase (as well as its tankmates) before making a purchase. If you see the slightest sign of disease, don't buy the fish. If the fish looks perfectly healthy to you, chances are that it looks perfectly healthy to the store's employees as well and they cannot be blamed if the specimen begins to show symptoms after you bring it home. A reputable store will not sell an animal that they know to be sick, but fish can often carry a disease without showing signs of weakness until the condition is fairly advanced.

You can avoid the risk of introducing a sick fish to your tank by keeping it in a quarantine tank for at least two weeks (but preferably longer) before adding it to your display aquarium. A quarantine tank can be a simple five or ten gallon tank with a bare bottom, a few simple (easily cleaned) hiding places for the fish, a filter, and a heater. Ten gallon kits with all of these items included can be purchased at many stores for about or you may save a few bucks by finding secondhand equipment.

A quarantine tank allows you to observe your new fish closely for signs of disease so that you can administer proper care immediately. Should your new fish become ill, a small, bare tank makes medicating cheaper and easier than it would be in a larger tank. This is because you will need much less medicine and big water changes will be more manageable. Also, using a quarantine tank protects your other fish from dangerous diseases and harsh medications.

This may sound like an unnecessary hassle, but if you ever inadvertently introduce disease to your display tank along with a new fish and lose most of your prized livestock as a result, you'll be kicking yourself for not taking this important step. A quarantine tank can double as a hospital tank, in case one of your fish becomes sick or is injured. It may also be used as a grow-out tank for fry, should any of your fish decide to spawn. So you see, a quarantine tank is a very useful piece of equipment, though many people insist on finding this out the hard way.