Yellow brownish leaves

This can be somewhat normal with the lower leaves at this age/stage of life, but are you feeding every irrigation? To me it looks like the beginning of nitrogen excess, but this usually affects leaves all over the plant, not just the lowest ones. Your plants are very green and a schedule of water/water/feed/water/water/feed if growing in soil is about right, so that your plants are being fed every 7-10 days. Any more often can lead to nutrients building up to burning levels in the soil quite quickly, especially when people do not irrigate to run off. At this stage, your plants nitrogen requirements are dropping, so if you are feeding no more often than I suggested, dialling back on one of your nutrients high in nitrogen may help, or even dropping it altogether and leaving all the other nutrients at their current rate may help. You could then rotate the dropped product with another, for example, say drop Biobizz Grow from the coming feed, then next time use it and drop Biobizz Heaven from the next feed, or something similar, but pick the one with the highest nitrogen levels to drop from your coming feeding mix first. Irrigating to run off, that is, water coming out of the bottom of the pot, is vital for preventing dissolved nutrients from building up in your soil mix. Once a build up occurs, it is very hard to cure, and flushing with vast amounts of water, while it may seem logical, can do more harm than good, as it often releases even more nutrient salts from the soil and accelerates burning. It will also wash out many other desirable things from the soil, making it a nutrient deficient substrate that then requires an even heavier applications of fertilizers to get your plants growing normally again, which can then lead to excess nutrient salts once again - a superb example of a "catch 22" situation, whereby solving one problem leads to creating another problem! So, in simple terms, either reduce the feeding frequency or the amount of nutrients given and always water to run off. Congratulations for posting this question early on, most people only ask when their entire plant is suffering and by then, it is much too late to help. Congratulations too on your excellent training, both indoor and with your "stealth" outdoor grow, very nicely done indeed!! Hope this helps,............ Organoman.