The SLP rigs require that you use an HPA tank that has a SLP (Super Low Pressure) regulator. All tanks have an integral regulator that takes the tank's raw pressure (e.g. 3,000psi.) and reduces it to the output pressure of the tank itself (i.e. the pressure that comes out of the tank and goes into the air rig). This pressure is then reduced further by the regulator on the air rig which the tank attaches to. The SLP tanks produces 300psi or less while "traditional" HPA tanks produce over 800psi. Therefore you can only use a SLP air rig with a SLP tank so as to not over-pressurize and break the air rig while an air rig like our MRS or Micro Reg can use either SLP or traditional HPA tanks.