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Cycling Safely - The basics of cycling are covered in this easy to follow article. Find out how to break-in your new tank the safe way.


Cycling is simply the process of breaking-in a new aquarium. Fish emit harmful wastes (ammonia) as a natural function of their respiration and excretion processes. Waste levels would build up to deadly proportions very quickly if left unchecked. Fortunately nature provides helpful bacteria to convert these deadly wastes into less harmful compounds. A new aquarium starts out with very few of these "good-guy" bacteria, so care must be taken to increase their numbers over time. The process of establishing these bacterial colonies can be very stressful to fish and generally takes about a month to complete. At the end of this break-in period a working/living "biological filter" will be in place.

The cycling process can be helped along by "seeding" the new tank with gravel, water and/or filter media from a fully cycled aquarium. It's a good idea to keep a sponge filter (or other secondary filter) running in an established tank for use as a starter filter in a quarantine, hospital or newly purchased tank.

BioSpira from Marineland Labs is the only commercial product that contains the actual bacterial colonies responsible for cycling an aquarium. Simply follow the directions on the product label. By and large, the concepts in this article still apply to cycling with BioSpira, as you are simply seeding the filter with an established bacterial colony. It should be noted that the effectiveness of other cycling products is questionable at best, because they do not contain the proper bacteria and may even encourage cloudy water & algae problems later on. The bacteria that we are trying to promote by cycling occur naturally and only need fish wastes, oxygen & time to develop. Products that adjust pH levels should also be avoided as they tend to cause drastic pH changes and cloudy water troubles as well.

You will need to purchase test kits for ammonia, nitrite, nitrate and pH. The only surefire way to know if your tank has cycled will be to watch the levels rise and fall as detailed in this article. Some manufacturers bundle all the test kits you need in one package or "master kit". Test ammonia, nitrite, nitrate and pH levels every day and log the results as you progress through the cycle.

It is perfectly natural to witness varying degrees of water cloudiness as you "break-in" your tank. This phenomenon is caused by bacterial colonies multiplying at enormous rates. The cloudiness usually goes away within a number of days and should not be a cause for alarm.

Fishless cycling (the process of adding pure ammonia to build up bacterial colonies) is outside the scope of this article and will not be covered here. This method of cycling is growing in popularity but you must be willing to work with an aquarium void of fish for as long as it takes to cycle the tank.

Let's take a look at the cycling process in action and identify the keys to cycling safely:






Day 1: The cycle clock starts as soon as you add fish. Set the cycling process in motion by stocking up to 1/2 of your tank's total stocking limit using the hardiest fish that you intend to keep (do not cycle with a fully loaded tank or with sensitive species). Barbs, Danios and Rasboras are good first choices for cycling a tank.
Ammonia: 0
Nitrite: 0
Nitrate: 0

Day 3: Ammonia (extremely toxic to fish) is detectable and rising. Monitor your fish throughout the cycle for signs of stress such as loss of appetite, gasping, "flashing" or darting. Corrective action such as a series of 10% water changes* or a one time dosage of AmQuel** (10 drops per gallon) may be in order.
Ammonia: rising
Nitrite: 0
Nitrate: 0

Day 5: Ammonia levels will begin to peak and fall. Nitrites (a dangerous but less harmful compound) are beginning to rise. Some fish may become stressed and fatalities may occur. Corrective action as described on day three should be taken if necessary.
Ammonia: peaking
Nitrite: rising
Nitrate: 0

Day 8: The first phase of the cycle is completed as the bacteria that converts ammonia to nitrite has been established. At this point in time ammonia is being converted to nitrite as quickly as it is being produced.
Ammonia: 0
Nitrite: rising higher
Nitrate: 0

Day 14: Nitrite levels have peaked and your fish may again show signs of stress. The use of aquarium salt (up to 1 teaspoon per gallon) or a series of 10% water changes* may provide needed relief.
Ammonia: 0
Nitrite: peaking
Nitrate: 0

Day 27: Nitrite levels are still elevated as the second phase of helpful bacteria begin the process of turning nitrites into nitrates. Continue to monitor for signs of stress.
Ammonia: 0
Nitrite: falling
Nitrate: present but may not be detectable

Day 29: The worst is behind us now as the second phase bacteria begin to process nitrites as quickly as they are produced. Nitrates (only harmful in higher concentrations) are now detectable.
Ammonia: 0
Nitrite: almost nil
Nitrate: detectable

Day 30 and beyond: Both phases of bacteria are handling wastes as quickly as they occur. The tank has cycled and you have a working biological filter! Nitrate levels can be maintained optimally (5 to 10 ppm) with 10% weekly water changes, or 20% every other week. You may now finish stocking the tank by adding a couple of fish per week until fully stocked. Water parameters may now be monitored weekly or bi-monthly.
Ammonia: 0
Nitrite: 0
Nitrate: must be kept under 40 ppm


Notes:
* Water changes do not inhibit the cycling process unless the gravel or filter media are disturbed. Water changes are useful if needed to keep pH stable and to dilute dangerously high ammonia or nitrite levels.
** AmQuel does not inhibit the cycling process because it binds ammonia making it non-toxic to fish but available to helpful bacteria. AmQuel does require the use of a salicylate based ammonia test kit. Nessler reagent based kits will show false-positive readings for ammonia if used with AmQuel.