If it were me, and I were using a sandblasting abrasive as a substrate, I would go with either a glass bead-type abrasive or something like black magic, which is an inert coal-slag type of abrasive. Now, when searching for the right grit size, I would assume that bigger is better, as that will reduce cloudiness and ph changes that might occur. Larger grit size also means that the substrate is less likely to get compacted, which would be unhealthy for your plants, if you have any, and less likely to have anaerobic spots develop.
I'm not sure if the grit size is similar to sandpaper grit, with 00 being the most coarse up into the 1000's for the finest, but I would assume that either 0 or 00 would be the right size (if we're talking grain size in sandpaper terms...)
