Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
Difficult to be specific about depth of sand which may induce the formation of gas pockets. Depends a lot on how fine-grained it is and how much it compacts.
Generally speaking though, it seems the experience of many aquarists is that sand less than 2" or 2.5" deep gets enough oxygenation to preclude anaerobic pockets from forming, whereas sand over 3" deep has a much greater incidence of this occuring.
3" or less seems to be a reasonable safe point in this regard, while still providing sufficient depth for plant root development and growth. But the larger the grain size, the less heavy compaction, and the more oxygen will reach the greater depth of the sand.
BTW Wendy, where are getting your white sand - what type of store ?