What's wrong with my sativa?

I've had problems with this plant since day one. I've got 2 indicas that have received the same treatment (the best of my newbie knowledge) and they are doing fine. (I hope)

Here are pictures of both plants.

The sativa's leaves have been thin for a long time and although I know that's normal for a sativa, this looks too thin to me, but I'm a beginner, so...

Also, I've been reading on flushing (my girls are pretty much ready) and I've read so many pros and cons that I'm completely confused. Yes? No? Doesn't matter?

So the first pic is the main cola on the sativa. Looks okay, but waaay behind the indica. In the 2nd pic you see the sats leaves are curling up and looking burned although I've not given this plant anything different from the others.

The last 2 pics are of one of the indicas. They have just done terrific. No muss, no fuss.

I'm guessing it's close to harvest for these last two as the hairs are starting to turn amber, that's why I was asking about flushing. Otherwise, once they start changing color, is there a way to know when they are actually ready to harvest? I know about checking the trichs, but I'm in Europe and the shops here sell these cheap little magnifiers with lights for $30 bucks. I'm too broke for that.

There are no cons to flushing it is absoulutely nessessary!!! You must flush with pure water for at least 2 weeks before harvest. If your smoking it the weed will leave a burning numbing sensation on your lips and tongue and will taste salty . If your selling it and you don't flush, you are part of the reason that most marijuana connoisseurs will refuse to smoke commercial buds. The only benefit of feeding to the end is a tiny amount of added weight....but who wants a lot of shitty weed!!!!!!!!!!!

Sativas almost always require LESS ferts than indicas. You definately need to back off w/ the ferts, water with clean water for a week and then add a smaller dose of nutes. Sativas almost always finish later than indicas so that is nothing to worry about, so expect another 4-6 weeks for the sativa (what genetic is it, do you know?). The indicas could probably go at least 2 more weeks and as I said before.....JUST GIVE THEM WATER! The best cannabis gardener I have ever had the pleasure to meet always says: "If you think they are done.....wait a week!

that Sativa doesn't look anywhere near done to me. that cola still has a lot of fattening up to do. Sativas always take longer than Indicas to mature.