Hi Wito
It's good that you are using some of your rock and gravel from the old tank, it is full of bacteria and life that will really kick start the cycle in your new tank! But just by moving it over and disturbing it you will have die off in the rocks and gravel and therefore you will still have a (hopefully!) mini cycle in the new tank.
Personally, I would do a very large water change in the old tank and use as much of that water as possible to fill the new tank. There are two reasons for this. Firstly you want to get as much bacteria as possible established in the new tank. You will move a lot over with the rocks and gravel from the old tank, but by using the water from there as well you will be adding even more to the new system, which can only help with the mini cycle you will most probably have. I also don't really see the point of using brand new, fresh water to cycle a almost brand new tank! Secondly, and most importantly, your old tank will still have your livestock in it, but suddenly you have removed a lot of biological filtration ( rocks and gravel). This may also start a mini cycle in the old tank because your livestock will still be producing the same amount of waste as before, but you will have less effective processing of it. So by doing the large water change you will hopefully be going into this mini cycle with water that is as pristine as you can get it, and I wouldn't skimp with this either because all your livestock will still be in this tank!
I would also skim quite wet in the old tank to try and pull out as much waste as possible until things start settling down. You could also maybe try using some SeaChem Stability in the old tank to help with this.
Well that's my 2 cents, good luck and post pics!
