im glad you said it was the ones on the bottom and not the ones on the top. my plants do that too. its actually a good thing. i think its because they dont get much light so the plant figures it for useless and starts to drop them so it can have food for the parts that need it the most , i.e. the new growth.

you do want to watch how much stuff youre adding to your water. cannabis has a certain TDS factor or EC its pretty much the same. Too much stuff in your water and it's too full of crap and blocks it from getting through the veins. its another type of lockout. so dont add too much stuff. usually for me if i want to raise my ph i just add tap water instead. but yes the most important part is keeping the TDS in the correct range just like pH.