Hey there! Make sure to pH after you mix the nutes. Sometimes its good to let the nute sit in the water for a while to "stabilize" and you may find it is really at a different pH than you expected. and if you have to flush with plain pH'd water with a pH around 7 until the runoff is in a good range then let dry out and go back to your regular feeding schedule. when you do go back to the feeding follow run-off and make sure it stays in a good range. It may be something to do with your soil. but definitely try to get it back up with just plain pH'd water. and that should tell you weather its the nutes or something in the soil it self causing it to lower. Happy Growing!!

Try to ph your water after you mix nutrients in. Nutrients can low your ph. If you are ph-ing your water before and not checking after you have added your nutrients this may be the problem. I hope you can figure it out ph is so important. Cheers.