Use old water or start fresh?

[ScubaSteve]

Originally Posted by parkinsn

You can take a few "scoops" of your sand to get your new sand going. Just dont x-fer all of it.

But in all seriousness, this is the way to go. Whenever I transfer my tank I get new sand and add about a few cups of the old sand the "seed" it.

Just as a counter point to this, I know a guy on here who rebuilds his tank regularly and washes the sand to re-use it. He, however, is doing this with a 20G where it is much, much easier to do a really good job of washing the sand.