Hello, farmers. Is this dangerous?

Its not dangerous, give plants littke rest from nuts check runoff its is over 1EC u should give them only water until EC will not drop below 1EC

This is burning from being waaaaaaaaay over fed, plants should be a healthy dark green, not purple/black green! Reduce your nutrients, especially any with nitrogen...........either the amount or the frequency. Very vague question though, you may know what it is, but a little more information doesn't cost anything.

Sometimes three blades leaves can be genetics. Sometimes it can be an indication that it's revegging. Check for any light leaks happening during lights off. Sativa strains tend to have thinner leaves than an indica strain. If it's a sativa it could just be genetic. Plant looks healthy otherwise. What's the strain?