on how much makes an inch it depends on your tank dimensions theres some calculators for it somewheres on here.i have a 55gal 48x13x20 and im putting a 4inch sand bed.ive had estimates from 105-130lbs.i didnt have southdown either so my bed costed a bit more i had to use aragamax sand i believe it was and it was about 25$for 30lbs