I'm very confused about "Cycling".

[Odder]

I have an established tank with fish that are doing fine. I've never done any cycling, and I still don't know much about it.
Under what conditions must you cycle your tank?

 

[Sgooosh]

I have an established tank with fish that are doing fine. I've never done any cycling, and I still don't know much about it.
Under what conditions must you cycle your tank?

before you start stocking the tank
youve already naturally cycled in the established tank

 

[Essjay]

A tank should be cycled before fish are put in it. I have read your other thread where you say you find it confusing, so I'll go right back to basics (you may already know all this, so my apologies if you do).

Fish excrete ammonia, it's their version of urine. Ammonia is poisonous to fish, but in a cycled tank there are bacteria which eat ammonia and turn it into nitrite. This is also poisonous to fish, but in a cycled tank there are more bacteria which eat nitrite and turn it into nitrate. This is not as toxic as the other two and in a cycled tank, weekly water changes are done which remove this nitrate. Cycling is the term we use for the process of growing these bacteria and a cycled tank is one which has grown all the bacteria the tank needs.
A brand new tank has virtually none of these bacteria, and they are very slow growing so it takes several weeks to grow enough to eat all the ammonia made by a tankful of fish, and the nitrite made from that ammonia.
It is safer for the fish if we grow the bacteria before we put fish in a tank, and we do this by adding ammonia from a bottle to feed the bacteria to get them to grow. This is called fishless cycling.
It is possibly to use fish to make the ammonia but this is hard work because the fish keeper has to do a water change every time daily tests show a reading for ammonia or nitrite higher than zero - this could mean a big water change every day and there is still the risk of harming the fish. Because there are fish in the tnak from the start, this is called fish-in cycling


You already have a fish tank, so that will already have enough bacteria to support the fish you already have. There will be bacteria in the filter media, and if the tank has been running for several months, there will also be bacteria on every surface in the the tank - on the tank walls, on all the decor in there and on every particle of substrate.
You can take about a third of the media from the tank you already have and put that in the filter of a new tank. The old tank will soon make up the numbers, and the new tank will have bacteria added to it immediately. The problem is that you can't know just how many bacteria are in that media. If you are over cautious, it is better to then add ammonia to the new tank to make sure there are enough bacteria to make the tank safe for fish; or you could add just a few fish to the new tank rather than fully stock it.
Whichever approach you take, either ammonia or fish must be added to the new tank as soon as the old media are moved over to feed the bacteria in the media.


The other thing that helps is live plants, especially floating plants. Plants need nitrogen fertiliser - farmers etc add nitrate to their crops to feed them. Aquatic plants prefer ammonia for their nitrogen. If there are live plants in a tank, they will also take up the ammonia made by the fish, and they don't turn it into nitrite (they turn it into protein). Floating plants are particularly good at this. If there are enough plants the tank doesn't even need any bacteria.
So taking media from an existing tank, and also putting live plants in the tank will almost instantly cycle a tank.

In your other thread, you mention setting up a new tank for baby guppies. Since they are so small when they are born, it is quite easy to set up the new tank for them by using mdia from the current tank and if you don't want to bother with plants growing in the substrate, even leaving a bunch of anacharis to float on the water surface will help - and the fry would love to hide in it.

 

[Ichthys]

A tank should be cycled before fish are put in it. I have read your other thread where you say you find it confusing, so I'll go right back to basics (you may already know all this, so my apologies if you do).

Fish excrete ammonia, it's their version of urine. Ammonia is poisonous to fish, but in a cycled tank there are bacteria which eat ammonia and turn it into nitrite. This is also poisonous to fish, but in a cycled tank there are more bacteria which eat nitrite and turn it into nitrate. This is not as toxic as the other two and in a cycled tank, weekly water changes are done which remove this nitrate. Cycling is the term we use for the process of growing these bacteria and a cycled tank is one which has grown all the bacteria the tank needs.
A brand new tank has virtually none of these bacteria, and they are very slow growing so it takes several weeks to grow enough to eat all the ammonia made by a tankful of fish, and the nitrite made from that ammonia.
It is safer for the fish if we grow the bacteria before we put fish in a tank, and we do this by adding ammonia from a bottle to feed the bacteria to get them to grow. This is called fishless cycling.
It is possibly to use fish to make the ammonia but this is hard work because the fish keeper has to do a water change every time daily tests show a reading for ammonia or nitrite higher than zero - this could mean a big water change every day and there is still the risk of harming the fish. Because there are fish in the tnak from the start, this is called fish-in cycling


You already have a fish tank, so that will already have enough bacteria to support the fish you already have. There will be bacteria in the filter media, and if the tank has been running for several months, there will also be bacteria on every surface in the the tank - on the tank walls, on all the decor in there and on every particle of substrate.
You can take about a third of the media from the tank you already have and put that in the filter of a new tank. The old tank will soon make up the numbers, and the new tank will have bacteria added to it immediately. The problem is that you can't know just how many bacteria are in that media. If you are over cautious, it is better to then add ammonia to the new tank to make sure there are enough bacteria to make the tank safe for fish; or you could add just a few fish to the new tank rather than fully stock it.
Whichever approach you take, either ammonia or fish must be added to the new tank as soon as the old media are moved over to feed the bacteria in the media.


The other thing that helps is live plants, especially floating plants. Plants need nitrogen fertiliser - farmers etc add nitrate to their crops to feed them. Aquatic plants prefer ammonia for their nitrogen. If there are live plants in a tank, they will also take up the ammonia made by the fish, and they don't turn it into nitrite (they turn it into protein). Floating plants are particularly good at this. If there are enough plants the tank doesn't even need any bacteria.
So taking media from an existing tank, and also putting live plants in the tank will almost instantly cycle a tank.

In your other thread, you mention setting up a new tank for baby guppies. Since they are so small when they are born, it is quite easy to set up the new tank for them by using mdia from the current tank and if you don't want to bother with plants growing in the substrate, even leaving a bunch of anacharis to float on the water surface will help - and the fry would love to hide in it.

Agree with all of this, good stuff, except you don’t need to add an ammonia source straight away when you move media. The bacteria can go a week or two without food (but you might as well feed them...)