If you've ever had a goldfish as a kid, and woke up a few days later to find him belly up, your goldfish most likely fell victim to the ammonia cycle. Fish waste, and decaying uneaten food produces ammonia, which is toxic to the fish. When starting an aquarium, the first thing you need to do is cycle the tank.
Start off by filling your tank with distilled water, or treated tap water (there are many products that will remove the harmful chlorine from tap water.) Run your filter for 24-48 hours with no fish. After you've done this, you can put in a few fish to start the ammonia cycle. Goldfish or Danios are good to start with, as they're very tolerant of poor conditions, and they're cheap.
After 8-10 days, ammonia levels will peak, and at this point the bacteria in the tank will start converting the ammonia to nitrites, which are also toxic to the fish. Keeping live plants can be very beneficial to the tank, as they absorb nitrites, and also introduce oxygen to the tank.
After another 10 days, the nitrites will start to convert to nitrates. Although nitrates are mostly harmless to fish (except in very high levels), nitrates can contribute to unwanted algae growth in the tank.
Once you have ammonia and nitrite levels in check, you can start adding more fish. Here are a few more ways you can help prevent toxic ammonia and nitrate buildup in the tank:
- Don't overfeed your fish. Overfeeding will cause them to produce more waste, and any uneaten food that collects on the bottom of the tank will rot, and contribute waste to the tank.
- Ensure you have good coverage of gravel on the bottom of the tank. Bacteria growth on the gravel will help remove waste products. Be sure to use a gravel vacuum to clean up fish waste and uneaten food from the bottom of the tank weekly.
- Don't overstock your tank. Having too many fish will mean more waste is being produced than your plants and good bacteria can remove, eventually leading to toxic ammonia and nitrite buildup. A good rule is one inch of fish for every gallon of water.
- Do partial water changes weekly. Refreshing 10-20% of your water every week will help reduce waste buildup in the tank.
- Clean your filters often, and replace them as needed.