Super Lemon Haze Issues

Hello RIU, I'm trying to help my SLH get over some issues. It's 8 weeks old in a 5gal pot with ffof and light warrior in a 2:1 ratio. I haven't checked the ph of the soil but the other plants that have used it turned out loads better than this one is at the moment.
It's under a 400w hps, about 1.5-2ft away.
It's been getting progressively worse for about 5 days now and I'm not sure how to treat her. She only gets fed r.o. (Watermill Express) water, and her last watering was about 4-5 days ago, so her soil is still pretty saturated.
Not quite sure if she's deficient in a certain nute, if checking the ph is crucial right now, if I over watered, or if it's something I haven't learned yet.

Would flushing help perhaps?

Any help would be awesome, thank you!

Ghs SLH i grow is a hungry strain....i feed mine 1100-1200 ppm from a couple weeks old in DWC with great results. I run them in Bcuzzz soiless mix too without the same results. Its not the easiest strain to keep happy. Im guessing its a deficiency somewhere and possibly underfed. Im no pro...just going by my experience with the strain

Thanks for the quick reply; I'm also using the GHS strain.
She's certainly not easy to please. I think I'll try repotting her into more soil in case it's underfed