Yeah, Imma go a completely different route on that one and say that I am POSITIVE it's nute burn. I had a young plant do the SAME exact thing (leaves angle down, leaf edges curl, brown spots appear...)
I would water the plant with plain ol' distilled water for at least a week (or untill leaves aren't angled down, and growth speeds up again) because otherwise, if you keep nute-ing it, it will stop growing completely and get worse.
If this helps: take note that the already damaged leaves will not go back to normal, but all new ones that sprout after the fix will be burn free. If this does not work, and the burn stays or gets worse (and you aren't using ANY nutes) then get a bag of the MOST GENERIC potting soil you can (as it will likely be the most nute-free ... a 20 lb bag for like $3) and transplant it, and continue with a week or so of just distilled water watering. (I guarantee THAT will fix it)
Yeah here's a pic of the nute burn I had, and another of the plant a week later (after I did exactly as suggested you do)... Notice on the second pic that the leaves that were damaged grew bigger, but did not look any better... while the new growth was flawless. This should happen to yours as well.
