The nitrogen cycle is the process that breaks toxic nitrogen waste products in an aquarium into less harmful components. For this cycle to develop, beneficial bacteria that feed on these waste products need to grow in the aquarium’s filter system. Introducing fish to an aquarium without a healthy nitrogen cycle in place is a bad idea — build-up of waste chemicals can put major stress on the fish, even potentially killing them. Thus, “cycling” is something that every new aquarium owner needs to do to ensure the health and safety of his/her fish.
CYCLING WITH FISH
Set up your aquarium and filtration system. To start, you’ll want your aquarium completely assembled and filled with everything you want in it, besides the fish. See our articles on setting up freshwater and marine aquariums for more information. Below is a brief checklist of things you’ll want to do before getting started — this may not match all aquariums perfectly:
- Assemble the aquarium
- Add substrate
- Add water
- Add air stones, air pumps, etc.
- Add plants, rocks, etc.
- Add filtration system (and/or protein skimmer)
- Add heater
Introduce a small number of hardy fish to the tank. Your goal in this cycling process is to populate the tank with fish that produce waste but can survive the initial high levels of toxins long enough for the beneficial waste-processing bacteria to grow. Thus, you’ll want to pick a variety that is known for being a good cycling fish and start with a small number. Later, once the bacteria have grown, you can slowly add more fish of different types. Below are just a few good choices for cycling fish:
- White Clouds
- Zebra Danios
- Cherry or Tiger Barbs
- Pseudotrophius Zebra
- Banded Gouramis
- X-ray Tetras
- Most minnows
- Most guppies
FISHLESS CYCLE
Assemble and prepare your tank. For this method, we’ll start with a fully-assembled tank, minus the fish. However, this time, we won’t add the fish until the entire cycle is completed. Instead, we’ll add biological waste manually as we monitor the water level and wait for the cycle to complete. This method requires a lot of patience, as it requires you to wait for the organic material you add to your tank to decay and start producing toxic waste products. However, it’s often considered a more “humane” option as it doesn’t expose fish to ammonia and nitrites.
Add a sprinkling of fish flakes. To begin, drop just a few flakes of fish food into your tank — about as much as you’d use to feed your fish will do. Now, simply wait. Over the next few days, the flakes will begin to decay and release waste products (including ammonia) into the water. Make sure bio filter is installed and working.
Add fish gradually when ammonia and nitrite levels are at zero. After about six to eight weeks, the ammonia and nitrite levels should decrease to a level that’s so low you can no longer detect them, while nitrate levels should plateau. At this point, it’s safe to add your fish. However, you’ll want to add your fish gradually. Don’t add more than a few small fish at a time and wait at least a week or two before introducing your next batch of fish. Consider cleaning the substrate with a siphon hose before adding fish.
USING MATURE FILTER
Since cycling a tank can easily take up to six or eight weeks, aquarium owners have long been looking for ways to shorten this process. One proven way to do this is to introduce bacteria from a tank that’s already been cycled to the new tank. Since you don’t have to wait for the bacteria in your tank to start growing naturally, your tank should cycle quicker than it otherwise would. One great source of bacteria is a tank’s filter — simply switch the filter media from the established tank to the new tank for a potential boost. Try to use filter media from a tank that’s a similar size and has a similar amount of fish. Mis-matching your filters (like, for instance, using a filter from a tank with just a few fish in it to cycle a tank with a greater number of fish) can leave you with greater loads of ammonia than the bacteria are able to process right away.
Have live plants in the aquarium. Living plants (as opposed to fake plastic ones) typically speed up the nitrogen cycle, especially if they’re introduced from a mature tank. Not only can plants carry beneficial bacteria (just like the substances above), but they also pull ammonia out of the water directly to use in a biological process called protein synthesis. Fast-growing plant varieties (like, for instance, Vallisneria and Hygrophila) tend to absorb the most ammonia.
Add small amounts of salt to freshwater tanks. If you have a freshwater tank, adding a very small amount of salt can help your fish stay healthy when toxin levels are highest at the start of the cycling process. It does this by reducing the toxicity of nitrite, the intermediate chemical in the nitrate cycle. However, you’ll want to use only 0.4 ounces per gallon of water at most — any more can be very stressful for freshwater fish. Be sure to use certified aquarium salt — table salt isn’t formulated for your tank and may hurt your fish.
JAMAICA ORNAMENTAL FISH 