Hi gamwar and Welcome to the freshwater beginners section!
If you have other tanks then there is no need to perform a full fishless cycle. Instead you can perform what we call a "Clone" operation. You simply need to remove biomedia from your mature filters on the other tanks and use that to "seed" your new filter. The principles of Fishless Cycling that we try to teach will help you "qualify" the new biofilter and ensure that it will have the least chance of mini-cycling on you when you move the fish in.
First, its quite important to not take more than 1/3 of the total volume of biomedia from any individual mature filter that you have already running another tank. Taking only 1/3 should ensure that you will not even see a blip in your test results on that tank (I'm assuming you are using a good liquid-reagent based test kit to determine your ammonia, nitrite(NO2), pH and nitrate(NO3) readings on a regular basis and recording them in your aquarium notebook, right?)
Often (unless its the exact same model filter) you have to get quite creative about how to remove (chop up etc.) the existing mature media and then how to successfully fit it in to a foreign filter box. The first thing to think about is that fresh media for both the old and new filters may need to be purchased to fill in for the cutting and moving about that you do. In your planning you will need to decide whether the biomedia you will transfer will just be loose media like ceramic gravels, ceramic rings or bioballs or such, or whether you will need to use scissors to cut sponges or floss pads. An important consideration is to make it a goal that the final setups maintain the "tightness" of the normal media as you had it before if at all possible. This may mean you need to cut a 1/3 replacement piece of sponge to be a tiny bit larger than what was taken out for instance so that it will fit back in with a tiny bit if tightness but not so much that it would close up the holes of the sponge. Does that make sense?
The mature media should be kept wet with tank water at all times during the process of course. You want to give your bacterial colonies the best chance of survival and the least disturbance to their physical structures (bacteria build tiny calcium structures within their biofilms to help channel water (and thus oxygen and ammonia) in a way that they can reproduce more efficiently.) Of course, all this takes place on a microscopic scale, so there's no need to be paranoid about handling media really.
Prior to transferring the mature media in, its preferable to have already started dosing the tank water with 4-5ppm of the pure simple household ammonia that you used in your previous fishless cycles. If you need to obtain more, the members can help you pretty easily locate some depending on which continent and country you are in (Boots for UK, Ace Hardware for USA usually.) The test kits we usually recommend are the API Freshwater Master Test Kit (this is the one most of us like and use the most) and the Nutrafin Mini-Master Test Kit or there are the Salifert kits which are actually more accurate and used by advanced aquarists. All of this is easier than it sounds from me writing it.
Once the ammonia is flowing through the new filter and the mature media has been transferred you will need to give the bacteria a day or two to come out of shock from the move but you will begin logging your daily readings. An additional step you can add is to clean out the rest of the mature biofilter material (that will be staying in the other tanks) in the water of the new aquarium. This looks messy at first but the new filter will pick it right up. With mature media you should see the ammonia begin to be processed by the A-Bacs and some nitrite(NO2) produced (possibly) and perhaps you will detect that the N-Bacs have "taken" and are processing some NO2 into nitrate(NO3). If all this is working, you should be able to quickly move into your "qualifying week" where you verify (this is the test of any working biofilter) that 5ppm ammonia can be reduced to zero ppm ammonia and zero ppm nitrite(NO2) within 12 hours of when the ammonia was dosed and do this repeatedly for 5-7 days in a row. If either toxin spikes then you know something is wrong and you start the week over again. At the end of the successful week you do a standard down-to-the-substrate water change with good technique (conditioner at 1.5x dose and rough temperature matching with your hand) and introduce your first fish stock within the day.
So what does this buy you that is different from plunking your fish in? To them, its all the difference in the world. A fish trying to swim in ammonia and/or nitrite is similar to us trying to breathe in a garage filled with car exhaust, its a life and death situation, even at low concentrations of the problem substance. If we don't truly know whether we have a working biofilter, we risk permanently damaging them and unfortunatly they don't give visual clues. By contrast, when we give them a qualified environment, we know our fish have the best chance possible in the transition to their new home.
Good luck and I hope this helps. With practice a "clone" should become a skill that is second nature.
~~waterdrop~~
