"I did very light watering..." I just wanted to say that normally you want to completely wet the soil (10% runoff is a good indicator that it's uniformly wet), then let it completely dry (not "completely," but almost until it's too dry and the leaves wilt).
This is a seedling, which is a little different, more sensitive to being too drenched or too dry. But, it seems like new growers hear "don't overwater your plant" and think that means "don't give too much water." They'll dribble a little in every day, which never lets the soil dry enough between waterings. It also creates uneven moisture (dry pockets). To me, the "don't over water" rule means "wet it (substantially) and forget it." Let it go through complete wet/dry cycles. A drench is good, as long as it's allowed to dry out.
A good way to know when it's dry enough for watering again is to lift the container. It should feel disturbingly light. You can keep another container full of medium (never watered) and compare what they feel like. But, what I do is just let the soil dry enough until the leaves wilt. Lift it, and learn what "too dry" feels like. I wouldn't do this to a seedling nor a flowering plant. It is a stress. But, in veg, the leaves will bounce back within 20 minutes of watering. It's not a terribly bad stress in veg. (It's a tradeoff. One stress to avoid the ongoing stress of watering too frequently. Not letting it dry enough.). When you know what that feels like, you can lift the container and wait till it gets within a few hours of that level of being dry. To me, that's one of those things you can't imagine until you do it. It's really amazing how dry the soil can/will be when the plant looks like it's thriving, not thirsty, not wilting. You have to see/feel it yourself to know. (But, you'll need to wait till you have 3-6 nodes, in full/thriving veg. You don't want to do that to a seedling.).
One big reason to let the soil go through complete wet/dry cycles is that the ph will move a full point. If it's kept too wet, it limits the ph range the plant experience. That limits the nutrient availability. Organic matter starts to adicify when kept wet (think of peat bogs). Suddenly, instead of a full point swing from 5.6 to 6.8 being capped at 6.0, it start going lower due to the acidification (being kept too wet). You quickly start having a 5.2-5.6 range, and lower.
Anyway, I just wanted to mention that. Whenever I see someone say "I lightly watered," I feel like they might misunderstand what "don't overwater" means. The volume should be heavy (10% runoff). But, the frequency should be fewer. It seems common for new growers to treat it like a houseplant, giving a sip frequently. That causes problems.
PS: If the problem isn't nutrients in the soil, it should make it. Cannabis is very hardy. I've done things that I'm surprised the plant survived. Seedlings are more sensitive. The best thing to do is leave them alone. (I wouldn't have transplanted it. A large container isn't bad. You just have to water it less frequently. Much less frequently. A small container is better. But, once you're in a large one, I wouldn't downsize it that way. That seems risky). Don't kill it with kindness. That's what usually happens. If you can let it grow itself, it should recover (unless the soil is too hot).
