Sometimes you just gotta bear with them. Acros vary wildly in growth rates based on a number of factors from flow, light, nutrients, species, morph, and a hundred more factors I'm forgetting. I run crazy high flow in my tank, so mine encrusted like mad until they are anchored well enough to take off.
Once they hit that sweet spot, believe me; They'll take off.
Once they hit that sweet spot, believe me; They'll take off.