Does this look like pH problem? (PICS)

I have three plants, different (unknown) strains.

All in the same soil with same ratio of perlite, coco fiber, worm castings. (standard, cheap, crappy, potting soil)

Just started feeding nova grow.

From the start of the grow one of the three plants has looked worse than the other two. They are all watered with the same water and nute solution.

Leaves are lighter in color, kinda small, showing signs of chlorosis.

I suspected a pH problem with the soil being too acidic. Measured it after watering yesterday and it is about 6. Maybe this one type of strain doesn't do well with the acidity and the others do?

Here are the pics:

The sick plant has a leaf attacking fungi (100% sure about that). The plant was probably stressed at some point and the fungus took hold then. It will still grow and the fungi probably wont hurt yield that much, but I would recomend u toss it or quarantine it before it spreads to the others (if u can afford to). If the others are already showing signs then just flower them all out. Symptoms appear first at lower leaves and work their way up the plant.