I think that is the one you need, yes its says they mositure resistant, that is the reason they use them for building houses, here in Belgium they use it as the bottom stones to build up. They don't let the watter trough. (if you understand what i mean) ;)
It's hard to find cheap ytong in the usa. I looked for it in large chain stores (home depot,lowe's, ect...) and all I get are blank stares when I ask about it. Some companies sell it but you have to buy a truck load.
Travis Perkins sell really nice Aerated blocks near where i live, they are white and contrast really nicely with the Ants. less than a quid for one and you can get discounts like Steve said.
breeze block
breeze block not the same. sorry mate
What I always called Breeze Block is actually "Celcon" - I think Breeze Block is a generic name like "Brick" or "Hoover".
I've used Celcon for my formicariums & it does the job well - water soaks through no problems....
Chalky
Jewson call the Top light blocks.