[lpsreefer]

The only thing the new sand with do is make ur water cloudy for a while. As long as you seed the new sand with ur old sand.
And use ur old water. You won't have any cycle.
Here how I would do it.
Put the new sand into the new tank.
Do a regular water change on ur two smaller systems.
The water you take out put into ur new system. I would do 50%.
Then add all your rock/ coral and fish over.
Since it not a new setup.
Ur using two smaller one into one big one I would even worry all that much.
New sand is good! Just a cup of sand from ur other system to seed and ur golden.