Why do my plants only have that light greenish yellowish look at the top and why is one of my plants also having those sick leaves at the bottom?

2 of my 3 plants are a bit yellow-ish at the top since about a week. Plant 1 also had a couple of sick leaves at the bottom that I did remove. Those leaves had brown/dark spots, felt dry like paper, had very purple stems and did smell more like hay. More info in my report.