I would be curious if newer growth imporved with a slight light strength reduction. Even 24 hours is noticable if you take lots of pictures or have a good memory. The curve of the leaves looks like the recent light stress in my tents.
Slabreal raises a valid point you will get a large variation of advice on here some helpful some not so much. Im not going to attempt to diagnose your plant youll get plenty of peeps to chime in on that but you should get yourself this lux meter to help with your lighting UNi-t btu lux meter its like $30 dollars it really helps with light distance and gives you a fairly accurate ppfd reading. Also this par meter is $500 aud and compared to top end devices this is excellent value and has been reviewed and tested with apogee par meters with very similar results. If i were you i would think back to when your plants were healthier and did you change anything like lighting, feed strength any enviromental changes watering practices etc. Good luck
Too much water would be my assumption, but you say they were light so dont know, when we have that much soil and a plant thats not growing optimally, the water stays way longer than you think, personaly id leave it to get bone dry, its always easier bringing a underwatered plant back than an overwatered plant, but hard to say without doing the watering myself. You can do an easy ph test too, sometimes it helps. The other thing could be if there was an accidental change in the light schedule? Dunno let us know
I checked my soil ph and it was 5 or under from nutes, so ive added calcium carbonate to raise it slightly i dont ph the water only the soil my plants are in. As a gardener for 20yrs now ph in soil can be an issue
@Loudpack516
What are you feeding the plant and how often? Ive seen some of my plants do a similar thing when the nutrients in the soil are basically used up. I usually top dress the soil and give the plant 4-5 days before I mess around with anything else.