Hi, let’s try to work through your issue step by step.
Dark leaves
These often appear when the plant is getting too much nitrogen. Please check which of your nutrients contains nitrogen and reduce it as soon as possible.
Pistils
They look normal. This slight brown coloring can actually be caused by the light being too close. Try to keep a distance of 20–30 cm. If you can, measure the PPFD value of your light. The pistils will keep coming back regardless.
Spider mites
Unfortunately, if you have a problem with them, your harvest is at risk. From my experience, getting rid of them completely is very difficult.
Before flowering, you can treat them well with neem oil or a nettle tea spray.
You can also try tying a damp cloth to the end of your vacuum hose and carefully vacuuming them off.