Hi smyth19
That's what I do.
It's better if you can take a piece of the media from your filter, rather than use squeezings. The bacteria you want are actually clinging to it, more so than in the muck that will come out, although I wouldn't rinse it out first. If you can transfer a plant, there are additional bacteria on it as well.
Most of the beneficial bacteria you want are on the top 1/2 to 3/4 inch of gravel, so this is what you will want to transfer. They are clinging to it, so give it a good vacuuming before you use it. There is no need to move the dirt that has collected there. It will only make a mess.
I do this kind of thing frequently, so I try to keep an extra 10 gallon tank available and use the same gravel in all my tanks. That way if I need a tank in a hurry I can just make a little "clone" off my 55 gallon. This works well and causes no harm to the big tank. Just replace the gravel and media with clean and the bacteria will soon multiply and replace what you took out.
Only thing I would not recommend is stocking it heavily. If you are just using it for a breeding tank, which means only a few fish, it will work out great. If you were to do this to set up a well stocked tank, I would suggest adding any more fish gradually enough so that the bacteria has a chance to multiply and handle the load.
Good luck with the breeding!
