Jack Herer,Holy Grail,Pineapple Express2

runoff potentially has more dissolved minerals than what you originall administered... due to evporation between irrigations. This could impact pH. So, runoff can potentially be higher and not be a problem. Being in soil, there's other possiblities tht would cause such a change. the types of fertilizers for soil often need microbes to process what is given before it is plant available... since tht stuff is too lage or otherwise won't go into roots, it remains behind and could potentially build up over time if providing more than what the microbes can chelate/fixate, whatever the term is called. The key here is it is healthy. keep an eye on it. you could try to pH-adjust what you irrigate with to counteract any swing in pH if it starts to show some symptoms... if it remains healthy i'd chalk it up to 'normal' for your current set of numerous related variables in your garden at the moment. Looks healthy and no N issues, which becomes less available per concentration at lower pH. Believe calcium is another that will quicly show you symptoms due to an acidic shift in pH. anyway, runoff and soil slurries should be a bit off from what the actual pH and EC of your soil is. as long as it doens't keep shifting further, should be ok in context of healthy plants.