Pics wud help a lot. How old are your plants. wot temp do you have and what stength nutes did u use. Also which leaves are turning yellow. The very bottom leaves often go yellow after a few weeks. It happened on most of mine, if this is the case its not that much to worry about, although i'm not 100%
A little nute burn can lead to a lot, be careful rainmaker. Good to see you still growing by the way.
Always err on the side of undernuting.
not good at all