muratic acid can speed up the curing process, but i expect can weaken the rocks as well.
when I made my rocks, I bought these big blue tubs from walmart and filled them w/ a mix of crushed shells, southdown, and carib sea special grade. when I had my rock mixture all done up, is would apply the mixture in a pleasing way, and then add some sand, a dripple here, a dribble there, so on and so forth, always being sure that there were places where wet aragocrete touched.
in hindsight, I wish I had put in some 1/4 inch pvc or broken plastic clothes hangers for strength, because a lot of my cooll designs were to fragile and couldn't support the weight of another rock on top of them, (I probably had the mix off slightly as well)
anyhow, I only have one piece of it in my tank right now, and I don't think anyone can tell it's fake.
Oh, I also put in bits of spaghettie, and angel hair, and mixed in some epsom salts, all of which eventually dissolve (and once you wash out the sand) you get a very natural looking incredible bit of rock.
"Maybe in order to understand mankind, we have to look at the word itself: "Mankind". Basically, it's made up of two separate words - "mank" and "ind". What do these words mean ? It's a mystery, and that's why so is mankind." ~ Jack Handey