Ph drop in ocean forest.

I have an Autoflower 5th week and it started looking like it had nutrient deficiencies so I tested the pH and it was like 5.9. So I ran a s*** ton of light nutrient water with a pH of 7.4 through it and finally got the run off 6.5. Not sure if it will stay that way but it's a start. I have started my little plants for my outdoor grow in Fox Farm also and bought a s*** ton of Fox Farm soil. I need help on adding lime to my soil before I mix it up in my 30 gallon containers I guess. Anybody with any advice advice on how to do this would be wonderful also on how to add lime to stabilize the pH in my little Autoflower. And what kind of lime and how much.

ph is known to drop in ffof due to the fact they use bark as a filler. back as a filler is a sign of poor quality soil so id look around..