Emilya Green
Well-Known Member
The base pH of the medium when it is dry has nothing to do with the pH of your input fluids and it takes a while for the soil buffers to influence the pH of the incoming fluid. It would take moving huge amounts of water through that medium to even begin to wear down, or wash away, the buffers built into the soil to allow it to have that base pH and only very highly alkaline fluids (or acidic fluids for that matter) would start to slowly change the soil's base pH over time.
But here is the point that seems to be greatly misunderstood: When you water with a certain pH level in your incoming fluid, the sheer mass of that much water swamps whatever pH the soil might be set to revert to when it is dry, and the pH of that column of saturated grow medium has absolutely no choice but to assume the pH that you set the incoming fluid to... there is just too much of it and the 10:1 rule applies. The upward drift that occurs in the pH of the fluid in that container over time occurs for two reasons... the slow but constant interaction with the buffering agent, and as the plant uses up the acidic nutes in the mix, the pH begins to adjust upwards toward that which is left over, the neutral pH of the water itself.
