Healthy Fish: Six Steps to Prevent Disease in Your Aquarium   

An outbreak of disease can be disastrous in an aquarium, sickening and possibly killing an entire community of fish. The good news is that disease is highly preventable. All aquarium diseases come from either poor conditions in the tank or introduction from outside the tank. So how do you protect your fish? Whether you're keeping tiny neon tetras or a huge Oscar, you can follow these six simple steps to ensure their health.

1. Don't add fish to a new aquarium.

That sounds strange, but a brand-new aquarium setup is a very harsh environment for your fish friends, and any store that allows you to buy both a new aquarium and fish at the same time either has employees that don't know what they are doing, or they're counting on return business when those first fish die.

Why is a new tank hazardous? Properly conditioning water in an aquarium requires much more than adding treatment drops to take out the chlorine and metals found in tap water. An aquarium needs to build up a colony of bacteria that will help break down waste products your fish will create, providing biological filtration that isn't covered by the mechanical filtration system in your tank. Waste products create ammonia, which becomes toxic to fish very quickly. Until the water has the right bacteria functioning, the ammonia and nitrite levels will be out of control and you will have "new tank syndrome"-stressed, sick or dead fish. Once the bacterial colony is established, the ammonia will be properly broken down, first into nitrites, then into nitrates.

There is one solution to this problem: time. You are not going to have a beautiful aquarium full of gorgeous fish in the first day, or even the first week. The process of creating a bacterial colony is called cycling a tank, and it may take anywhere from 14 to 40 days (longer in a cold water tank). Set up the aquarium, then use one of two methods to start the cycling process:

* Add one or two very hardy fish, feed them properly and wait. The fish will produce ammonia, which will attract the right bacteria from the air. Those bacteria will break the ammonia into nitrites, which will attract other bacteria to break the nitrites into nitrates. Use water testing kits regularly throughout this process. When the kit cannot detect ammonia or nitrites, and the nitrate levels are increasing, your aquarium has completed the cycling process and it is safe to add other fish.

* If you don't want to take a chance on the lives of two fish for the cycling process, you can add pure ammonia directly to the aquarium instead. You'll want to do an internet search on fishless cycling for a complete guide, but basically this method involves adding up to five drops of ammonia per gallon of water in your tank, adding more as the levels drop, until the nitrites are at the maximum level on the test kit. Once the nitrites fall to undetectable on the kit and stay that way for at least a day, the cycling process is complete.

2. Quarantine all new fish.

Patience is required in most aspects of keeping an aquarium, and adding new fish is no exception. Never add fish to your tank until you've had them at your home, adjusting to your water conditions in a separate quarantine tank for about a month. This gives you time to watch the fish and spot any signs of disease that the fish has brought with it from the pet store. If the fish is sick, you can treat it in the quarantine tank without ever exposing your other fish to the disease or the medicine.

When adding fish to a new aquarium (fully cycled, of course), add fish slowly. The tank bacteria will need to adjust to the new levels of waste put out by more fish. Also, dumping an entire community of fish into the aquarium at once will stress the fish. Start with whatever fish is going to be your primary occupant (if you're including schooling fish, start with the school) and gradually add more fish over the next few weeks.

3. Don't add too many fish.

There is a standard rule for aquarium health: keep no more than 1" (2.5cm) of fish per gallon (3.8L) of water in the tank. If you have a 20 gallon (75L) aquarium, you can keep a maximum of 20" (51cm) of fish in that tank. More fish means more waste for your filtration system to try to keep up with, plus the fish become stressed when the water is more polluted and more crowded. Stressed fish = diseased fish. If you want more fish, invest in a larger or additional aquarium.

4. Don't overfeed your fish.

Feed fish on a schedule. Some species need to be fed once a day, others as often as three times a day. However frequently the fish need to eat, try to keep the feeding time consistent, and then feed only as much as they will consume in five minutes. Excess food breaks down into excess waste, setting the stage for disease to move into the tank. Another reason to stick to a feeding schedule is this: fish beg. They learn, like other pets do, that you bring food, and they will beg for it even if they are not really hungry. Ignore the begging and feed them according to your schedule.

5. Use only feeder fish you have grown.

If your fish eats smaller fish, keep a separate aquarium and breed your own feeders. Feeder fish bought at pet stores are typically kept in horrible conditions and are very likely to introduce disease to your tank.

6. Change the aquarium water regularly.

Aquarium water has no way to refresh and revitalize itself the way a lake, river or ocean does. You have to do that. Make a habit of removing up to a fourth of the water in the aquarium every week or two, replacing it with fresh, conditioned water.

If you follow these steps, your aquarium should stay clean and your fish should remain healthy.

About the Author

Morgan Bancroft has been sharing his knowledge with FAO readers for the past three years. Find more articles by Morgan at Fish Aquariums Online.