I think your plants look fine. Perfect grows are rare. I know a 20-30 plant grower that always has yellow tipped plants. The tips are the most sensitive to imbalances. Old sun leaves will turn yellow and die as the plant deems necessary. The thing I noticed the most is how orange/red your lighting is. Are you using the bulb that came with the light set? I switched to a hortilux metal ace after my clones were doing really shitty under a 15 dollar stock phillips bulb. The orange/red is used in construction, and while it still works to grow under, a bulb with more blue light would guarantee you better growth. It's worth the 100 bucks.