I've done this before. You have to go slow, adding sand either only in very thin layers or only in one spot at a time. If you add a lot of dead sand over your entire live sand bed, you risk killing much of your aerobic bacteria (more sand, = less oxygen reaching the existing bacteria, get it?). You can either add a small amount of new sand over the entire bed, like 1/4 to 1/2 inch at a time, or you can just add small piles in the back of the tank and spread them out later after the bacteria has had a chance to colonize.
I added more to the back of my 110 about 6 months ago. I used a spare piece of 2-inch pvc that was long enough to reach the bottom of the tank and still stick out the top. I funneled dry sand through the pvc and used it as a guide to put the sand right where I wanted it. I hardly had any clouding at all....worked like a charm.
