I've been trying to adjust the ph of my 3gal bucket filled in coco thats currently at 7.5...way to high. So i flushed it with RO ph'd at 3.7/3.8 but for some reason the ph of the container plant will not go down. So far i've already poured 10 gallons over it but it's sticking to 7.5. I just replaced/calibrated my ph pen so that cant be the problem. Its other solution phs correctly...i checked it agains a buffer solution. how do i bring down the ph?