Soil grower here, but maybe try Hydrated lime as an option. It will balance the ph if that is the issue. A few tbls per gallon of water and let sit for a couple hours. Siphon off the solution, leaving the left over powder at the bottom. Water and then check your root ph in a day or so during next watering. Repeat if thing start to improve. It’s not an instant fix. If not then go for a complete flush with light nutes in the last gallon.