i have 6 plants in 3 gallon fabric pots under a 675 watt led.temps are around 72 lights on and 68 off, light is on 18-6, feeding sensi grow coco at 13 mls per 4 1/2 gallons, using ro water. im having problems with keeping my medium at 5.8.-6.0, i stick my soil pen in and ph is around 5.0- 5.4. when i water with 5.8 the ph does not go up, so i watered at around 7 ph and got my medium to 5.9 - 6 but then the next day its back down. why is it drifting down and not up? pretty much my waterings have been of ph of 6.5 or higher. what am i doing wrong.