yea man.. once plants get older they will often shed their younger leaves.. it usually happens in flowering when you have some type of deficency, usually nitrogen.. but its not too big of a problem if they are yellowing slowly.. try giving it some Nhey J, quick question.
do plants kindof start to auto prune themselves in early flowering. since i started floweirng my very bottom leaves have started to yellow, wilt and fall off.
i water with epsom salt and im almost positive it isnt PH related.