A product that is intended to help your aquarium cycle faster. These are not always good for your aquarium. It is better to use other methods to cycle your tank.
What is and how to do: fishless cycle
Fishless cycles are the most humane way to correctly cycle a tank. Using fish to cycle a tank is inhumane and provincial\narrow-minded. Even if the fish does not die during the cycle process the stress can definitely negitively affect the fish`s lifespan.
Fishless cycles also tend to be quicker than other cycles because there is no fear of killing innocent fish, no loss of investment, no water changes, and, simply, more flexiblity.
A fishless cycle involves mimicking fish excrements, or making the clean tank dirty. The best way to do this is by adding drops of pure ammonia to the tank, and using a test kit, looking for an ammonia spike. On the first day add drops of the ammonia to the tank, until you get a clear ammonia reading when you test the water. For each following day, add the same number of drops as on the first day. Over the next week, monitor your ammonia, nitrite and nitrate levels. After about 2 days the ammonia level should decreases and the nitrite level should spike. In the next 3 days the nitrite level should also recede and the nitrate level should rise steadily from then on. Once your tank has read: 0 ammonia, 0 nitrite and 20-50 nitrates for a few days then you know the cycle is complete and fish may be added. The drops of ammonia should no longer be added at this point. Also, remember to always add fish in incriments. Pure ammonia can be found at hardware stores. I have never used this method myself, so look at other aquarium fourums for more information.
This simulated cycle can also be started by adding tropical fish flakes to the water. As the flakes decompose the release ammonia, which starts the cycle. You can also use shrimp. Just wrap it in some paper towel (to keep it together) and add it to the tank. This method can be messy however. As the shrimp decomposes it can cause algae blooms that cloud the water, and can also heavily pollute the tank if it is not removed at some point.
Overall the best way to cycle a tank is through the pure and ammonia drops and "seeding" a tank. Seeding a tank involves adding gravel and/or filter material and/or water from an established tank. An established tank is simply a tank that has already been cycled from several monthes, usually 6. This tank has countless colonies of benefical bacteria, so when gravel, filter material or water from this established tank is put into the new, clean tank the benefical bacteria is jump-started. This will radically reduce the time it takes to cycle a tank. However, make sure this gravel/filter material/water comes from a healthy tank, with no disease/illness. By sharing material with other tanks you run the risk of introducing unwanted elements to your tank. Therefore, these materials should not come from a local pet store, and only from a health tank.