Cycled?

Discus and angelfish breeders keep their pairs and growouts in empty tanks except for a sponge filter. I haven't investigated their tank setup procedures, but I have a question about it.

If you have a filter on a cycled tank then move the filter to a tank freshly filled with treated water, is the new tank cycled?

If you did the same thing except used water from the cycled tank to fill the new tank, would that be better?

I have my own opinions and experiences with this. I want to find out if they follow what other people think.

I'm currently running 4 Aquaclear 500s and 1 Aquaclear 300 on my 110. I'm curious as to how effective and safe it will be to set up new tanks with the extras.

I've always taken a sponge filter from one tank and moved to another without giving it much thought and never had any problems. I was curious as to how they get by with doing that considering the bio load is relatively high with keeping the pairs well-fed. I find that I'm second guessing a lot of what I've done in the past since I've seen so many people having problems where I never did. I have rarely had even a case of ich, much less all these other diseases people are reporting. The times I've had something though, one was viral and the other was bacterial that caused the most losses. I'm sure I'll get my confidence back once I get all my tanks up.

No different than fish, usually 4-6 weeks. But that's not this topic. I'm specifically talking about bare tanks.

I'm thinking that in order to be accurate, a filter must come from a tank that has a very similar bioload otherwise it will be thrown into a mini-cycle which would be harmful to the new tank inhabitants.