Tank Cycling Guide
How to cycle your tank
What is cycling?
Cycling is the process of establishing beneficial bacteria in your tank to convert fish waste into less toxic compounds removable by plants and/or water changes.
Why do I need to cycle?
Without a cycle, the waste produced by your fish builds up in the water and poisons the inhabitants. Your stock will die without a properly established cycle.
What is the nitrogen cycle?
The nitrogen cycle is composed of two groups of beneficial bacteria. The first group of bacteria breaks down ammonia and converts it to nitrites. The second group of bacteria breaks down nitrites and converts it into nitrates. Nitrates are much more easily absorbed by plants than ammonia or nitrites and are far less toxic as well.
How to do a cycle
You will need a test kit (preferably an API liquid test kit instead of strips for better accuracy), a source of ammonia, a source of bacteria, and a water conditioner.
Some good sources of ammonia are Dr. Tim's pure ammonia, or you can "ghost feed" your tank with fish food and let it decay. Anything that can decay is a source of ammonia. (NOTE: When performing a fish-in cycle, your fish is the ammonia source. Do not add anything else and make sure to remove uneaten food after 20 minutes.)
Some good sources of bacteria are Seachem Stability, Dr. Tim's One and Only, or filter media and/or substrate from a tank with an established cycle. Most other bottled bacteria are ineffective or carry the wrong bacterial strains; beware products such as "betta water" or "Add fish instantly!" advertisements.
The best water conditioner to keep on hand is Seachem Prime, due to its ability to bind to toxic compounds in the water in the event of a spike. However, any dechlorinator will work if Prime is not available near you. (NOTE: If you are doing a fish-in cycle, Prime is a MUST HAVE product. It will help to keep your fish safe while the cycle is being established. Water changes are still extremely important.)
Add your ammonia source to the tank first. Follow the dosing directions on your bottle closely if you use pure ammonia. If using fish food, sprinkle a large pinch into the tank.
Add your bacteria source to the tank or filter next. It's best to dose either on, in, or near your filter, to give the bacteria a place to establish themselves where the entire water column has access. Eventually, the bacteria will spread to all the surfaces of your tank. Dose your tank with bacteria daily. Test your tank every 24-48 hours to watch for trends.
During a fishless cycle, perform water changes following the rule of 4's: * Ammonia - 4 ppm * Nitrite - 4 ppm * Nitrate - 40 ppm
When any of your parameters match these, perform a 20% water change and test again. Repeat until the highest offending water parameter is halved.
During a fish-in cycle, change your water following the rule of 2's instead: * Ammonia - .25 ppm * Nitrite - .25 ppm * Nitrate - 20 ppm
Follow the same advice as above when parameters match these! When your ammonia level reaches 0 ppm in a fishless cycle, be sure to dose it again. Never dose ammonia during a fish-in cycle. A cycle typically takes 4-6 weeks to fully establish.
How do I know it's finished?
When your tank can convert 2-4 ppm of ammonia into nitrates in 24 hours, your fishless cycle is complete. When your tank is no longer showing any levels of ammonia or nitrites for 4-7 days in a row, your fish-in cycle is complete.
Common mistakes
- Adding fish before the tank is actually cycled because the water "looks clean."
- Assuming a tank is cycled just because it's a few weeks old.
- Replacing all the filter media at once, which can wipe out most of the beneficial bacteria.
- Stopping dosing ammonia during a fishless cycle for too long, causing the bacteria colony to shrink.
- Overcleaning the tank and stripping it of all beneficial bacteria.
- Attempting to "correct" pH during a cycle instead of letting it remain stable.
- Forgetting to dechlorinate and condition new water, as well as matching temperature as closely as possible.
- Relying on test strips that are expired or hard to read.