Straight kalkwasser, or the alk component of a 2 part liquid system or lemon juice or white vinegar will all work....I even heard that Tabasco hot sauce works (probably the vinegar in it) Hmmmm...... I wonder what ever posessed the person to try tobasco sauce in the first place? I also heard of a method where yu take a small piece of styrofoam bead and push it into the hole the aipstasia is growoing out of. You can pack it in pretty tight and trim flush with rock, and it smothers out the pest.