Hanna Instruments Water Resistant Portable pH EC TDS Temperature Meter Irrigation Filters Fill your recirculating hydroponic system Foliar Applications Fill your recirculating hydroponic system reservoir with water and add equal amounts of House & Garden Aqua Flakes Part A and House & Garden Aqua Flakes Part B to the tank to achieve the required strength and mix well Use the Stealth RO Replacement membrane when your flow rate decreases or your PPM increases The HI9813 6 features the Hanna Instruments CAL CheckTM that will allow the user to know when the probe needs to be calibrated or replaced A variable TDS conversion factor ensures that your results are right the first time