PH problem

is the plant showing issues? ph testing of runoff is as much art as ... it's more art than science, lol. There are so many things that will cause it to deviate even if nothign is wrong in the substrate itself. Isn't this a bottom feeder? If so, what you have to worry about is the EC that results at the top of where the water absorbs to. this is where problems can occur. That's where toxic buildup can occur. pH drift is indicative of a poorly buffered soillless/hydro nutrient product. Also, expect some offsets from what you pH balance your fertilized water to. What matters is the equilibrium that results in teh rootzone, not the exact pH you buffered to. Same with EC. A consistent offset is easy to work with. read the plant and react. Vast majority of nutes enter plant through "mass flow", but some are activley transported around the root. Which can result in a shift of solutes in the water that occupies the medium. This could change the pH. Usually in a soilles context you rely on 10% runoff from the top-down and that mitigates this effect. With a bottom feed, it doesn't mitigate this much at all. It's a poor way to water in a soilles method, imo. if it continues to shift, give a top-down watering with your fertilized water and get 20% runoff. This will reset it. May have to do this every X weeks etc. you'll have to figure that out as you go.