Ok, here is how I personally (now after a very experienced man told me how) cycle my tanks!!! You take as much water from an already established tank during a routine water change, and put it in your new tank and fill it with the rest fresh water! Also the VERY best thing you can do is swap filters with a established tank and you let it run for like 2-4 days and BAM you put you fishy freinds in!!!! And the best part is NO CHEMICALS!!!!!
Like Christian said, and what is the bacteria in the used filter media going to eat until you put in the fish to create a bioload?You may as well fill a tank with dechlorinated water, put fish in and all will be well, right up to the first ammonia spike and if they survive that, the nitrite spike will get them. Putting a bacterial culture in clean water with no nutrients for the bacteria to consume and then grow is just about doing the same thing. I just cycled a 30 gal. for a friend, by doing this, I put four feeder goldfish in the tank, 2 days later and daily after that I squeezed the good good brown liquid from one of my AC500s into the new filter media and after one week had ammonia and nitrite levels of 0.Now the feeder goldfish are going into my pond and my friend can start GRADUAL STOCKING of the fish he wants to keep.
Actually we have done this with 4 tanks and NO fish loss, but whatever you think is right... go hard!!! I personally do NOT like adding chemicals and we have lost less fish doing it this way than we did doing it the "normal" way... I also will NEVER add amonia to our tanks!!! fish or no fish!!!
As for what the other tank does with the new filter... the fish and water from that tank establish it quite fast... the bacteria continues to eat off the bio filter for a few days and then you add some fish (and YES do it slowly to avoid spikes of any kind) and the bacteia will then feed on theire waste.
Yes you can also put your new filter on an established tank and get it ready that way b4 putting it on your new tank... we too were sceptical of this method so we tried it on the small tank first and when it worked did it on our 90 gallon and it worked... The best thing is it works fast so if you have a big problem with a tank and need to move fish FAST I personally feel this is the way to go.
BTW We have had cichlid for 2 years and they have ACTUALLY never been happier then they are now with absolutly NO chemicals with exception of aqurium salt!!!! It's only a suggestion though!!!
