It's Red Devil lye, which is sodium hydroxide, and you can get it from a chemical warehouse. You want to use sodium hydroxide as that is what kills the Apstasia. The product that Lowes sells is called Roebic Drain opener.
Drano will also work, as it contains sodium hydroxide, but contains other things too though they're not harmful to you corals, inverts or fish.
You want to use .5ml and put it right on the Apstasia, try not to spray it around.