Cyco Nutrients - Platinum Series - XL Gro StimPurified Phosphates Promotes Insane Root Growth! XL Gro Stim has such a powerful effect on plants that it only needs to be used once! It's formulated using something called super phosphoric acid, which is produced by reacting phosphates with sulphuric acid. Super Phosphoric acid provides a readily available and potent source of phosphorus that plants can easily assimilate. This is a particularly important feature, since phosphorus can often get locked