Originally Posted by Marinebeginner
...(Have been gradually reducing depth of crushed coral in preparation so its only 1cm deep max.
That was a good plan!...
Another thing you can do if you're worried about bumping the nitrates, is to remove a portion of the old stuff each day... replacing it with new.
Find something you can use as a barrier between the two... an old piece of plastic or acrylic, or whatever you can find... start at one end of the tank and remove some of the CC, then put in the sand with that barrier between ... repeat each day and take several days or a week to make the transition. You'll limit how much bacteria you remove, and give the new stuff a chance to seed a little before you remove more.
Then again... you could probably even skip the "barrier"... having a little crushed coral mixed in with your sand at the end of the process really isn't going to hurt anything.