Hello, I am using a coco fiber medium, which I've always heard is extremely pH friendly, and House and Garden nutrients in a top drip recirculating system. I mix my nute water, and adjust the pH before putting it into the reservoir. I changed the water yesterday, and when I checked it this morning the pH had risen from 5.7 to 6.8. I have no idea what would cause this.. any help would be great. Thanks!