Mixing sand

[Trabby]

We are currently running a 14g oceanic biocube. We recently aquired a second cube and have decided to fire it up as well. I bought a bag of carribsea arag-alive pink fiji sand. The sand in the running cube is much finer grained, I was wondering if it would be bad to exchange say 2 cups of the fine to put in the other cube and 2 cups of the coarser sand back into the established cube. Or is that going to cause havoc with water specs?