Woah everyone, step back breath and think.
First what are the signs?
We have lower leaf necrosis, so how does leaf necrosis happen ?
Excess or deficiencies in nutrients, which if fed too much or too little will happen, also pH lockouts can cause the same thing.
So whats the cause ?
Well the plants look "really" green but healthy otherwise and were just given there first dose of nutrients and weren't like this before "hmmmm i say".
Being that the plants are still early and that your biobizz looks like a pre fertilized "lite" mix which i have never used myself, but your plants were healthy and doing find on just water and look more than healthy in the pics so much so that personally i would be backing off the nutrients with how dark your plant is, i would personally say you over fed and locked/burnt the plant.
Adding anything will just cause more issues so just water for now with plain water and do so till you have slight run off, check the pH of the runoff just to be safe, but do this for the next week or so till the media lvls out and only when the plants start looking like they are needing some nutrients such as lighter green to boarderline yellowish leaves then start to add some feed back in to get nice looking leaves.
Pretty sure you just fed to heavy too soon due to the combination feed and pre fertilized mix and have started to lock the plant out either due to too much or pH.