Upgrading To 6ft Advice Re Sand/laterite Etc

hi
we have a 4ft community planted tropical that we want to change for a 6ft. we have bought the 6ft & now want to do it right. we want black sand for our new tank & ive read a bit about stuff called laterite or something like that that is good for plants on the bottom. our current 4ft has gravel substrate which although we've managed to grow lush plants in i hate & definately want the sand (esp for our corys & loaches to whisker through)

i really need advice on how to do the substrate to give our plants which will be uprooted for the change the best possible chance for recovery & new growth. our 4fter is looking the best it ever has so i think i might have cracked the 'growing plants with no co2 trick!!!' & although dreading changeover day cant wait to see the 6 fter in its place with loads more space for our fish.

any hints or advice greatfully received, esp on how much sand & laterite stuff we will need for the 6ft tank. its 18 inches high & 12 inches wide.
thanks
this is our 4 fter now

If you want to go low tech Tom Barrs guide to low tech is worth a read, I love your tank by the way to my eyes it appears very "dutch" in scape style.
If your thinking mid tech or even hightech substrates like ADA are great.
If cost is an issue www.theplantedtank.co.uk jamesc's site has a brilliant article on Akadama which is one of the cheapest superior substrates and ideal for this kind of set up, I don't know if it's any good for kholies or corydoras though.
Tropica's substrate would be a good idea below sand too, Supercoley used it to great effect.

Here is a substrate calculator

http/www.practicalfishkeeping.co.uk/pfk/..._calculator.php

You can have a layer of laterite then sand or you can mix it i think but that would only work with gravel unless you want a different tone of sand.
I like your tanks, very nice, i bet your new one will look better! Only crypts don't like being moved as they suffer from crypt rot so you should be ok.