Yellow leaves and brown spots - please help

Could be both. Definitely some deficiency there and a flush only exacerbated it, but if the overall ratios of nutes is off, could be necessary, but this is really late to try to fix it. The red you see is akin to fall/autumn colors you'd see outside, if you live somehwere with that season. It's probably due to cooler temps at night, but can also be genetic. I'd ignore this as long as your lights-off temps aren't dipping too far below 68F. Even 68F can bring it out, and colder will cause it to happen even faster. looks like some pale leaves down below, so probably low N at the least. would need more info to provide a proper educated guess. use an app to calculate ppms from your products you mix -- a good one should ask for dose of each and do all the math for you. believe hydrobuddy is one? Since you are probably a bit low on N i'd suggest a full diet of 120-130 N 40-60 P 180+ K 100+ Ca 75ish Mg 100+ S you may need more Ca than that. I have hard tap water and it likely adds a few ppms. Local variables will impact overall concentration you need, but this is a light mix and well-balanced. All you should need to do is adjust overall concentration. Your VPD compared to mine will impact rate of drinking. Higher vpd needs a lower overall EC. I tend to have a slightly too high VPD, which is why i feed around 1.2-1.3 and not 1.5 or higher. I still get 50-60g/sq ft, which is all you can do with ambient co2. Armed with that info, look at how you've fed the last month or so... is it drastically lower or higher? overall or individial concentrations, each matter equally. These nutes have a lot of interalted relationships - antogonistic and stimulative (mulder's chart). Ratio is more important than overall concentration, in my opinion. Easy to adjust overall conceeation. More difficult to adjust 1 nute without changing others, typically. Normally in flower i do drop N to 110 or so. 10-20% drop usually avoids any dark/glossy leaves late in flower, which are symptoms n-tox. Not all plants need this dip, but when growing 10-12, a few will for sure, so account for the low-probability because it's better than the alternative. Since your plant has yellow leaves at bottom and top, i'd wager your fine with 120-130ppm and there's not enough time for any buildup to occur at that feeding rate. Your buds look plump. Don't do anythign too crazy with so little time left. Make sure pH is fine before messing with nutes. Dostart diagnosing sooner, in future. be patient, but start figuring it out sooner.