I had a plant go super chlorosis back in April. I couldn't figure out the problem until one day, a week after the plant's leaves were bright neon green between the veins, I decided to check the medium it was growing in. Turns out, the soil was soaked and swampy, due to a peat moss pot never being removed before the plant was up-potted.
So, I scraped all the nastiness away from the roots, mixed up a batch of soil, and popped the plant in there. I didn't water it for a while and it slowly turned around. Now, it's one of my biggest plants in my grandaddy purps grow(P3, if you ever check the grow out).
It will turn around. Just be careful with it and make sure it gets everything it needs.
Good luck!