Only two of a buch of seeds that sprouted ended up surviving. One started flowering pretty early on, despite getting the exact amount and schedule of light as the other one (they shared a pot). The other kept growing taller then died without any signs of flowers.
The post pic is from ~2 weeks ago. At the start of this week, it looked like this: 
And the leaves just kept dying.
Today I decided to just harvest it. Here it is after cleaning: 
I don't know what strain this is, because I didnt label the seeds. But it smells very citrusy and I know there were some lemon haze and lemon skunk seeds among them.
What are the next steps? I've heard I should hang them somewhere to dry, is that correct?
Coco coir is notorious for holding onto salinity due to it's ideal CEC so if you don't get the low-salt stuff or you don't know if it is, give it a very thorough flush. In fact, I'd do that anyway just to be on the safe side.
I've never grown cannabis before (not a bit btw) but if your coir is too salty then I can't imagine cannabis is gonna take well to it.
(In fact, it shouldn't be all that hard to go media-free and this could eliminate some variables, but that's a topic for someone who knows what they're doing with a cannabis grow.)
Just make sure that you understand how to store a pH meter so you get accurate measurements. Unfortunately they are much more fickle and delicate compared to tools like thermometers.