hello, im buying a marine tank off someone this week end and it comes with 2 fish 7 kilo of live rock and 1 inch of live sand, it is a old tank so the sand has been in there for awhile, i was wondering if i would be able to add another inch of live sand which will be brand new from the shop, if i do add it should i mix it with old sand or should just place it over it before i fill the water back up, thank you

