This is the beginning of burning from over feeding and/or a build up of toxic fertilizer salts in the substrate.
It is not a cal/mag issue.
Give plain water for 7-10 days in normal amounts and at normal intervals, then when you resume feeding, reduce the strength or quantity of the fertilizers you are giving.
Your plant needs to use up what is already there before any extra fertilizers are added.
Your plant will be fine without being fed for 7-10 days, basically, 3 irrigations without fertilizers.
Giving 5 different "bud stimulants" does not guarantee resuults, pick one or two, that is all that is needed.
If wanting to use every product, swap them around, that is, give one or two, then next feed use the other one or two, then etc, etc.
Also, when growing in soil, a schedule of plain water/plain water/feed/plain water/plain water/feed works well, it is something I have been doing for close to forty years now and has been highly successful for me.
Also also, 18/6 is optimal, 21/3 is a waste of electricity and a stress factor for your plants, all cannabis plants need adequate "sleep", just like every living entity on planet Earth.