I am communicating with a fish breeder who says that fish are okay as long as there is fresh water (water changes) and surface agitation causing water movement and thus aeration. When they talk about cycling, they mean getting nitrifying bacteria to grow in your tank. This takes about 6 weeks. You can do it by adding sacrificial fish, or by adding a few drops of ammonia (representing fish waste) but it should be only "pure ammonia" sold by fish stores and not cleaning ammonia. Another way is a bit of rotting food. The "cycle" is that nitrifying bacteria (present in the air, in the ground, and all over) get into your tank by "floating in" which is true, or by you adding it. The nitrifying bacteria eat the ammonia, which they basically "poop out" as a second toxic material for fish called nitrites, this needs a second type of nitrifying bacteria that eats the nitrites and turns them into nitrates. At that point you get in the act and do a water change, starting the cycle all over again.
Quick ways to cycle. Add a water plant from a healthy pond or pond mud. This is a bit risky, but you get a load of already living nitrifying bacteria because they are already in that substrate (they move in water, but they live on the sides of things like rocks and wood and plants and the side of the plant, which is why people want to put porous material into their filters). Nitrifying bacteria doubles in size every 36 hours. And you only have enough to take care of the fish load you have. So if you have an empty tank, you got no nitrifying bacteria.
HOW do you know you are cycled or cycling? Get a water testing kit. What happens is you will add ammonia. test the water. The ammonia will begin to rise. Bad news for any fish, that is why they say use sacrificial fish. You need to water change more often if real fish are in there. Once the ammonia starts to rise, you should start to see some activity with nitrifying bacteria. In clean fresh (dechlorinated) water you will not have any nitrites unless you have polluted water. With the water testing kit, test for nitrites. If you have nitrites. With the tests you will see both ammonia and nitrites. Do a water change. keep the fish alive is the game here. If you are doing the ammonia drops (which I recommend), then add a few more drops (there are a certain amount per gallon that you must add). So ammonia will lead to nitrites, then after some time of only ammonia, and nitrites, you will suddenly seen nitrates. Every day test the water, twice a day if you can. Test the water, do a water change, add new water, then add more ammonia drops. So you should have all 3. Allow them to get as high as you dare. Bright colors. Then do a water change. The same let them build up. At some point they will all just go away. This is a cycled tank. It should show zero ammonia, zero nitrites and 20 or below nitrates. Once you stop adding ammonia the cycle will stop. You are then free to add fish but add them slowly.
Other ways to get a quick cycle. Doner substrate from a fish shop or friends with tanks. Old dirty fish tank water. It is kind of like baking sourdough bread. You provide the food (ammonia) the critters just jump into your tank (I think this is better done outside), and then they start the cycle. They eat, then that changes the stuff they eat, some more jump in, and they eat, that changes the stuff, and then some more critters jump in and make some more stuff, and then you do a tank change.
By the way, this makes your aquarium (glass box, rocks and so on) the largest living creature, because in order to take care of fish waste that tank needs to be crawling with these animals. Sorry for the long post.
