I have a 20 gallon resevoir and ive started using concentrated lemon juice to lower the ph, but after a few hours it goes back up. Any advice would be appreciated. thanks
Sounds like a lot of folks are having pH problems, and there's an easy answer out there - use better nutrients. Use nutrients that are designed to help you avoid the ups and the downs.
The pH Perfect® technology from Advanced Nutrients is killer, and it's guaranteed (I think) to keep your pH problems from, well, being problems.
If you have to keep taking drastic measures to change your pH, you need to find a new nutrient lineup - one that actually works.
good luck!