Superglue gel is safe to use. I just apply a liberal glob of the gel on the frag, submerge it in the tank and attach it to my rocks. As the superglue hits the water, it forms a skin on it, so when you do the attaching, give it a little twist to break the skin. Some on here apply superglue to both the frag and the rock, but i've had good luck just applying the glue to the frag.