Most say Superglue gel from Loctite. Works great. However I buy the generic superglue gel 2 bottles fro the price of one Loctite. Yellow package, says the original superglue. $1.79 for 2 in one package. I've tkaen to blotting my frags where I plan to glue with paper towel first. Then apply the glue and either stick it in the tank where I want it or glue it to a small piece of rubble out of the tank. Works well under water. Just be prepared that the tube has a lot of air in it. Seems as though you squeeze and squeeze and that last effort all the glue comes out in one go.