What's wrong with this plant?

[bluter]

looks good.

 

[jimiding]

I've had similar experiences. When I got sickly ones, I just moved them to the flower tent to see what happens. They always produced nice buds, but they were just sort of small with small yields. If it's bugs, most bugs don't fair as well once they start flowering and the leaves start getting sticky. Spider mites are definitely an exception to that observation, and you definitely don't want to introduce them to another tent. I use this cheap but pretty nifty USB microscope "Digital Microscope 1600x HD" to scan leaves for critters.