Yep, nutrient burning.
Don't stress it, pretty much everyone's done it at some point. But you should try to sort it out.
First of all, stop feeding them the nutrient you already have. Rinse the soil through with 3 - 4 x it's volume of tap water.
You then want to sort out the nutrient. If you've made a big batch of it and it's too strong, do you remember how much nutrient you put in it? Or do you have a pen to test it? If you can remember how much you put in, double check it's the correct dilution (specially if you were baked when you worked it out). If you know it's miles off, you'll have a better idea of how much to water it down. If not, try ~20%.
Plants that big going onto nutrient for the first time won't necessarily want nut at full strength, and almost certainly not the boosted strength. You can go for 50% and get them used to 100% over two weeks. 100%+a bit extra is only really good when you know they're super resistant or once it's really dumping energy in flowering.
As someone's already said, you'll get slight burns on smaller plants even if you use 75 - 100%. But they should only be on the tips of the leaves really. What you've got looks too severe for them adjusting.
Forget about the burnt leaves, it'll be kind of hard to see if they're burning anymore.
Watch the new leaves right up near the top. Watch the tips for any yellow'ing / browning, that's the first sign that they're not 100% happy with the nutrient and you should back it off as soon as it appears, because it'll inevitably get worse if you leave it. Yellowing could be a few things, but with your prior burn, it's almost certainly going to be nutrient.
Nutrient is a less is more thing. Once you incinerate a lot of good leaves, they're useless. Running it a few percent weaker won't slow things down, it will keep the energy producing areas of the leaves. At 100%, you should only increase it slowly and watching the plant for any stress.
Also, are you adjusting your pH? If not, you might want to check it out.
Is that soil and perlite you're using there? I remember those days. I might still do another soil grow, something about it seems more wholesome. Two things anyway! Is your soil packed down? It looks quite fluffy at the surface but it's easy to pack soil and that can waterlog it under the surface. Also, run to waste with nutrient on coir or soil, you'll want to think about flushing it in the bath every week or two so it doesn't end up rammed with nutrient.
The one in the bottom left looks like an Oak tree.
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