The Planted Tank Forum - View Single Post - cycling a filter in an established tank?
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post #17 of (permalink) Old 01-26-2013, 02:10 AM
Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Posts: 11,721
Read my answer to your other post. I included the complete instructions for the fishless cycle in that thread.
This will work to grow the same bacteria whether you want to keep frogs, fish, shrimp, snails, or any other fresh water livestock in the tank.
There are some notes about adding a starter culture of bacteria to jump-start the bacteria colony.
Here are some more notes:

Nitrifying bacteria grow in a bio film, stuck to surfaces. There is so few of them in the water that it is not a good source of starter colony. It is safe to do a 100% water changes on an aquarium and lose so few bacteria that there is not even a blip in the test results.
If you have an established tank with a cycled filter, you can add another filter, add filter media, or any other variation you want, hoping to grow some bacteria on it. You can remove from the cycled tank some of the hardscape, plants or other things, hoping to transfer some bacteria.
If the livestock level in the donor tank remains the same, then the bacteria population will remain the same. Adding more media for the bacteria to grow on will not increase the total number of bacteria.
If some of the bacteria grow on the new filter media, then you remove the filter you are removing the bacteria.
If you remove some of the hardscape items you are removing bacteria.
Keep on testing the established tank, and do water changes as needed until the bacteria colony recovers. I have removed as much as 25% of the filter media from a well established tank (several years old) and not had a problem. Note that 25% of the filter media is not 25% of the bacteria. The bacteria grow on many surfaces, in the tank, and on the equipment, so it might be as little as 1/8 of the bacteria.

But if your main tank is only a 5 gallon there will not be a whole lot of bacteria, unless the tank is WAY overstocked. You probably will not be able to take enough bacteria from that tank to support 3 ADF any more than you could add 3 ADF to the tank and hope for no mini-cycle.
If the tank is 'way overstocked' what will happen to the water chemistry when you remove enough bacteria for the new tank, but keep the same number of fish in the old tank?

No matter how you slice it your aquariums only have enough bacteria to support the livestock that is in there now. When you want to buy more livestock you need to grow more bacteria. Best and fastest and safest way to do that is with the fishless cycle.
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