hey there, your soil is too hot (too many nutrients) that's what's causing the yellowing of the leafs there, unfortunately there's nothing you can really do against that at this stage , just keep pushing through, but if you can i would start again with cheaper less amended soil. The reason i say that is that any kind of stress or shock when they're young basically makes them grow much slower for the rest of their lives. For now for sure you want to water with plain water and water really small amounts to make sure the water doesnt release too many nutrients for the plant to handle. watering just before lights on is a good idea because the temperature difference between night and day releases humidity in a similar way to nature at day break, like that's what dew is all about (idk if you know that word : basically condensation on the grass in the morning) and the plant is naturally programmed to absorb most of it's humidity in the first few hours of light. Hope this helps ! 🚀