I've seen a lot of questions about cycling so I thought I'd do a thread that basically explains how to do a cycle with your fish safely and effectively.
Any tank can be cycled but only tanks 2.5 gallons or larger will really benefit from a cycle. Cycling builds bacteria in your tank that help keep ammonia and nitrites produced from decaying fish food and waste from harming your fish. By doing this it will reduce the frequency of water changes you need to do to keep your fish happy.
Here is what you need to do a cycle:
Gravel (or any other substrate you prefer)
Decorations, plants, etc to make your tank look good.
A thermometer (in tank or digital kitchen)
Master Test Kit (liquid dropper kind)
Set up your tank the way you want it. Make sure you rinse all your gravel, plants, and decorations in hot water before adding them. Fill your tank with De-chlorinated water and bring it up to 76-82* before adding your fish. Make sure you acclimate your fish slowly to the tank water.
Care for your fish as you normally would... nothing changes here. Everyday test your water for Ammonia, Nitrite, and Nitrate. The first thing you will start seeing is Ammonia.. the others come later in the cycle. Anytime you see Ammonia in the test you will need to do a water change. Use your judgment to decide how big of a water change to do.
--Personally I do a 20-30% pwc (partial water change) for any reading under 0.50ppm and 50% for anything over 0.50ppm.--
After a while your Ammonia readings will spike. You will clearly see this as your test readings will jump really high from one day to the next. Almost immediately after you will start getting readings of Nitrite. Continue doing your water changes any time you see Ammonia or Nitrite in your tests. What is happening is a bacteria has formed that takes the ammonia and turns it into less harmful nitrite.. this is basically a half-way point in your cycle. Make sure you continue testing every day.
After some more time you will see a spike in your Nitrites the same way you saw in your Ammonia... and your ammonia will go way down and almost disappear entirely. Once this happens you will start seeing Nitrates. A different bacteria is now taking your Nitrites and turning them into Nitrates.. which your fish will tolerate. Continue testing and doing pwc's if you see any Ammonia or Nitrites in your readings.
One day you will test and you will get a reading of 0.00ppm Ammonia, 0.00ppm Nitrites, and 5-20ppm Nitrates. This means you are cycled. Continue testing daily for a week to 10 days to make sure your readings don't change.. if they do continue with your water changes and testing until your readings remain constant.
The cycle process can take anywhere from a few weeks to two months depending on several factors. Size of tank, bioload.. meaning how many live animals you have in the tank, and how much you feed can be influencing factors.
Once you are cycled you will have much fewer water changes. Depending on the size of your tank you may have 2 wc's a week to 1 a month.
2.5-5 gallon tanks need 2 pwc's of 50% a week with vacuuming during one of those.
5-10 gallon tanks need 1 50% pwc a week with vacuuming.
10+ gallon tanks need a 50% pwc every two weeks.. at least.
(These are not concrete but a basic idea of how many water changes per tank size)
Here are a few helpful hints:
-if you can get established filter media or gravel from a tank that is already cycled and has no diseases it can help speed up your cycle.
-don't get media from a pet store as their tanks frequently have sick fish in them.
-there are some commercial products that are supposed to help speed a cycle but they haven't gotten very good reviews among fish keepers in general.
-live plants can not only help your cycle but your fish in general. Be careful before you decide to do live plants because they will require extra work.
That's pretty much cycling in a nutshell. I don't think I left any major points out but anyone feel free to add or correct any mistakes.