The most difficult time in the life of an aquarium set-up is the initial phase, as the hobbyist waits on the system to cycle. Until this occurs, any fish in the aquarium are at risk to exposure to high levels of ammonia and/or nitrite that can reach toxic levels, killing the fish. Since the cycling process can take several weeks, the hobbyist must take great care to not add too many (or the wrong type of) fish. Unfortunately many people become totally discouraged during this time period and tear down the aquarium and either start over (to have the same problems again) or just quit the hobby. A good understanding of what is involved in the cycling of the aquarium can make the process easier to manage and encourage the hobbyist to “stay the course.”

When we say cycling the aquarium what is really meant is establishing the beneficial nitrifying bacteria to complete the Nitrogen Cycle in the aquarium. Fish (and other organisms) release waste products into the water as a result of respiration. The primary waste product is ammonia. This is a very toxic compound and even low levels (2 to 4 PPM) can lead to fish death. Fortunately, Nature provided a group of bacteria that utilize ammonia as their primary food source. This removes the toxic ammonia, but the waste product of these bacteria is a slightly less toxic nitrite. (Recent studies have hinted that nitrite is not toxic in marine aquariums.) Once again a group of bacteria come to the rescue and utilize the nitrite as a food, converting to the relatively harmless nitrate. Once these colonies of nitrifying bacteria are sufficiently established to instantly convert all the wastes produced by the fish, the aquarium is cycled. This is why it is important to start with just a few fish, allowing them to live in the aquarium for a week or two. During this time it is important to use a test kit to monitor the ammonia and nitrite levels. Ammonia should start near 0.0 PPM and peak somewhere between 2 to 6 PPM, then rapidly decline to close to 0.0 PPM. Shortly after the ammonia starts to peak, the nitrite levels should start to rise, peaking at 10-20 PPM. Once both the ammonia and the nitrite are back to reading 0.0 PPM, the aquarium is cycled FOR THE CURRENT fish load. At this time it will be safe to add a few more fish since the nitrifying bacteria will already have a good-sized colony and are not starting from scratch to handle the additional waste load. Patience is still the best method for adding more fish to an aquarium.

The procedure discussed above is the natural method of cycling the aquarium. Fortunately, several products have been developed to speed up the process of establishing the nitrifying bacteria colonies. These products can be a liquid solution of live bacteria (placed in “stasis”), concentrated liquid solutions or a dry (freeze-dried) powder. The bacterial starter is added to the aquarium and helps digest the fish wastes and promote the growth of the nitrifying bacteria colonies. The use of these products is not a license to immediately fully stock the aquarium with fish! Test should still be used to monitor the ammonia and nitrite levels to see when it is safe to add more fish. These products should be used after performing a partial water change or cleaning of the filters. They can also make a significant contribution to the recovery of the biological filtration system after the aquarium has been treated with an antibiotic compound to cure an infection on the fish.

The aquarium can also be cycled faster if rocks, ornaments or filters from mature aquariums are placed as part of the new set-up. Any of these items would be coated with colonies of the nitrifying bacteria. Even old gravel can be used when tearing down an older aquarium to replace it with a larger one. If the old gravel is not going to be used in the new aquarium, several cups of the old gravel can be put in a mesh bag and simply placed in the new aquarium or its filter system for a few weeks. Used with one of the prepared bacterial cultures, this represents one of the fastest methods to safely cycle the aquarium.

While not exactly part of the cycling of the aquarium, it is worthwhile to realize that the “cloudy white haze” that develops in new aquariums (New Tank Syndrome) or after a major disruption in the aquarium is related to the nitrifying bacteria. When these bacteria are not present or their mature colonies are disturbed, a free-floating type of bacteria will quickly multiply to eat the available wastes in the water. While this is harmless to the fish, in almost every case, simply waiting for the nitrifying bacteria colony to establish/re-establish will cause the cloudy haze to disappear. This process can take 5 to 10 days, so once again patience is required. Products made to “clear cloudy water” will usually be unable to clear the free-floating bacterial haze. They are designed to remove small floating particles of waste or even algae.

Stress Zyme, Bio-Boost and Cycle are liquid cultures with 100’s of millions of nitrifying bacteria kept in an inert state until added to the aquarium. Bio-Zyme is a dry powder form of the nitrifying bacteria. Also available are pre-colonize media. Nitrifying bacteria are grown on a porous media and then sealed in a jar flushed with nitrogen to place the nitrifying bacteria in an inert stage. These additions can also have a “pro-biotic” effect on the fish when introduced to a mature system. They stimulate the fish’s natural immune system to help increase the general health of the fish.

It should be noted that the type of aquarium décor and filter system can effect the establishment and efficiency of the nitrifying bacteria. The bacteria need suitable surface area to establish their colonies and water movement to bring new supplies of food (ammonia and nitrite) and oxygenated water to the colonies. The wet/dry trickle filter, Bio-Wheels and Fluidized filters all offer an excellent environment for the nitrifying bacteria. The use of medium to small gravel with an undergravel filter can provide a decent environment, but will require more maintenance to keep its efficiency. In a quarantine aquarium or breeding/grow out aquarium there will usually be no gravel for the bacteria to colonize, so the use of a Hydro-Sponge Filter can help provide the needed surface area for the nitrifying bacteria. Once established, the nitrifying bacteria will safely protect the fish from the toxic ammonia and nitrite wastes. The end product nitrate will be kept under control by periodic partial water changes.

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