Few of the leafs tips are turning yellow, not sure...

So there's a few things here , your in very very early stages of nutrient burn I would slow up on the nutrients dilute them a bit more and feed less frequently. You don't wanna be feeding them nutrients every single time in soil because the root zone will get to hot and a few things will happen you will burn your roots and your will cause nutrient burn in your plant . I'm also noticing a CalMg deficiency so I would likely start adding that to the feeding routine as well this will decrease the purple-ing stems in your leafs and provide the plant what it needs to grow more robust ! Given that pre flowers are showing up its time to PK boost as well , your going to want to do this for 2 main reasons 1) will help facilitate current buds growth 2) it will promote new bud sites . Don't be scared to give these ladies a good dose when you do give them water and nutrients just don't do it every feeding and always make sure you let your soil dry out before the next feeding so the root zone don't get hot I hope this info helps you on your journey to becoming a grow master !!! -Happy growing!