So, i see your grow is 8 weeks into veg? And i see you've mixed a blend of soil's like happy frog and ocean forest and 1 other. Those are very good soils and will carry your plants for 45 to 60 days, but after that you're going to need to fertilize them man. At first i thought it was a salt build up locking things out.
Your pH in your soil could be off. I say that because lack of fertilizer will NOT burn the tips of your leaves, which i can see they are all over your plant. You have what looks to be multiple issues which usually is a pH in the soil issue, or a Lock out situation due to salt build up in the soil. Since you haven't been feeding them outside of the soil supplied nutrients, it won't be excess salts causing lock outs. It's more likely your pH is not in range in your soil.
Lower leaves turning yellow and browning usually means the plant is robbing it's lower leaves of the mobile nutrients to use at the growth tips.
Your brown tips could be be nutrient burn damage, but not from over use of fertilizer, but rather a VPD problem. Meaning VPD is too high. If you have high temps and low humidity your plants are going to take up way more water and as a result, more nutrients than it needs which can damage your plants and actually result in nutrient burn.
Try to feed in a balanced nutrient mixture and pH it to 6.2 and see if your plant responds. Also, if your temps are high try to bring them down to 80F and get your humidity up to 60 to 70% until your plants are in flower. Then drop your temps to 75F if you can and reduce your humidity to 50%