Runoff PH too low

Y would you want to bring it up. And if you had nutrient lock. Any nutrients in that substrate will mess with any water u pour in and you will not get a real ph number For a real PH soil needs to have no nutrients and to know your soil PH you'll need a Soil PH tester not a solution tester. As soils pH changes with nutrients that's added to it. Not from the water that passes through it, as that's only picking up the excess nutrients and making a PH from that. But mainly you'll get a PH from soil run off. As that usually is a solid PH for soil. Just make sure to give more reg water feeds in between and any feeds you give the PH in that should be enough for it to be where you need it to be at. Good luck.