Yellowish leaf on one of the plants

Hey 👋 Definetly nutrience burn. Reduce your grow fertilizer, looks like overfed with nitrogen to me… but nothing too serious so far. 1-2 times only plain water, and you’re back on track. Enjoy the journey 👊🖖🍀

The yellow is the start of burning from feeding too much or too often.......... or both. In soil, a schedule of plain water/plain water/fertilizer works well in my experience. You should not be fertilizing in soil any more frequently than every 10 days or so and certainly not twice a week or even with every irrigation as some people try. Always water the entire pot and always get some run off, it is the only way to know that water has got right down to the bottom of the pot where most of the roots are and getting run off also prevents nutrient salts from building up, which can be another cause of yellow tips.......salt build up. Further to your diary questions, there is absolutely no need to defoliate your plants and I would also suggest "lollipopping" would be poinless on plants this size. Just leave them be to finish as naturally as possible and without any stress. Remember too........less leaves = less energy being made = less potential. Defoliation is hardly ever needed, except in extreme cases where controlling excessive humidity is a huge problem..........otherwise most people do it blindly because "everyone else does it" and without any actual knowledge as to how plants function and how detrimental it can be, all in the belief that somehow removing energy making leaves will magically make their buds grow bigger. It is a bit like removing a couple of spark plugs from your engine and then expecting increased performance. Buds do not need direct light to grow, just like how fruit does not only grow on the sunny side of the tree! LST is probably the most effective treatment to improving a plants' potential.

once you do gain that familiarity... you can calculate your elemental ppm or weighted % of mass from labels, if 'gauranteed analysis'. You can match that ratio and concentration ramp up with the same soil in future.. change the soil and you have to learn a new concantration and ramp up.

You should be patient and see how it progresses, but based on location and pattern of symptom i'd lean high sulfur at the moment, but there are other causes that fit the symptoms, too. low k or high p are other options that can cause tip burn, but other symptomsm would help delineate as it progressed. its good you are tracking ferts and such, but you are using a soil, so there's a bunch of unknowns. The dose you need to supplement may be different for someone else. It'll be useful info for you to gain familiarity with but most others won't ever have that familiarity unless they use the exact same stuff.