I heard Vinegar lowers the pH but after a gallon if it in my system my water still stays at 8.5-9. which is way to high for the plats to take up nutrients.

Any suggestions?

the pebbles we purchased came from the sea and it may be why the pH is high. it was completely washed though but some say the shell fragments may be causing high pH.

any natural ways to get the pH down to 7-7.5