its for a 24x8x8 inch tank about 20 litres.
AE says 3 litres for 20litres of water. but i was going to go for more as like you said you will always use more than stated.
but i just thought the leftover might aswell get used in the other tank as they get no ferts/co2 etc
thanks
chris
Well that's miss leading since substrate quantity is dictated by foot print rather than tank volume.
Your foot print is not too different from mine if I'm right, so go for 6l.
an after thought, ask sam (themoulus) or see if it says how much hes used on his nano I think he's used aqua soil.