Without cycling, you could not have aquariums. Cycling is a process that breaks down fish waste into less poisonous chemicals. Most often, cycling starts with a few hardy fish like guppies, to get the cycle started. However, you can take steps to speed the process and make it safer.
What is Cycling?
An aquarium is not a complete ecosystem. In real life, fish have so much water around them that they rarely are threatened by their own wastes. In a fish tank, another mechanism must break down wastes before they become poisonous. In your aquarium, various bacteria break fish wastes, particularly ammonia, down into less toxic chemicals. Managing your tank through this process is called cycling. Without cycling, it would be more-or-less impossible to keep fish in a tank for any length of time.
Cycling your aquarium involves three chemicals: ammonia, nitrate and nitrite. Your fish produce ammonia, which is toxic to fish. Helpful bacteria break the ammonia down into nitrate, then nitrate. There is a lag between the fish producing the ammonia and the bacteria multiplying enough to break it down. Cycling is managing your aquarium through this process. Ideally, you can introduce a few hardy fish, like guppies, into your tank and monitor the water levels until the nitrate levels reach zero. Then you perform a water change and add a few fish and repeat until you reach your tank's capacity.
There are several different way to speed the process, or make it safer for your guppies. One is silent cycling. In this process, you heavily plant your aquarium. Plants metabolize ammonia and other nitrogen products very similarly to the bacteria that normally help cycle a tank. Adding plants to a cycling tank can help protect your guppies, providing a safety net for the bacteria, speeding the process. However, plants are living things and require care. Dead and dying plants can make things much worse. Only attempt this if you know you can care for the plants.
Another option for your guppy tank is fishless cycling. In this method, you add unscented household ammonia to your tank and cycle it before you get your fish. This method has some advantages, particularly that you don't risk the first fish you put into your tank. You can also add all of your fish at once. You do have to test your water more frequently, since you will not have any indicator that something is wrong. The biggest drawback is that this method requires patience; you must wait until the tank is cycled completely before adding fish.