i would stay away from blasting sand and slag because it is rough on bottom feeders reguardless of what previous posters have mentioned. there are numerous posts of people loosing the barbells on difrent kinds of catfish including corys due to blasting grit. that stuff is purposly designed to be abrasive.
on a difrent note for a planted tank 55's are a lot harder to scape because they dont have a big foot print, there just real tall. 40b's are ideal for planted tanks, gives you lots of room to scape how you want insted of trying to cram everything in a 12inch area