Definitely from overfeed resulting to high ec build up in your substrate this happened to one of my ladies in my garden, just not as hungry as th rest, I use something called drip clean which acts like a magnet for salt particles to help free your root zone up as your have more then likely burnt your roots, this is a really easy problem to come across without using an EC pen. Also are you feeding Nutrients everytime you water? Personally I like to do feed-water-water then depending on EC levels of my run off either feed or water. In my experience with this problem drip clean helped me right out aswell. Back to drip clean it might look really expensive but you only need 0.4ml/gallon, hope this helps you out and I hope your ladies bounce back,
happy growing!👊👍