How do I test the pH & PPM/TDS in my soil/hydroponic growing medium? Fill a cup with warm, distilled water and add a few pinches of the soil. Stir for 30 seconds then dip your meter in it. I need to have reflective material to bounce the light back to the plants but I do not have a wall to hang the reflective material on. What can I do? I reuse my soil/hydroponic medium & I have noticed that each crop my yields go down and my plants look less healthy. What is causing this?