my ph was doing that when i had them in the dwc buckets. so i switched to 30 gal rubbermaid tubs that holds 8 plants each. and my ph has stayed the same since and that was 2 weeks ago. it started out at 5.8 and it's now at6.1 and from what i have read thats still in the range it needs to be in. i have 2 res filled to 22 gals each. and 1 at 10 gals i just wanted to see if there was a diffrence and all of them are staying the same. so i don't know what was causing the ph to do that. but when i went to a bigger set up it stoped so