The leafs started to look yellow in the middle whe...

Hi @TheMan! The curly/wavy leaves tells us that this seedling is suffering from heat+high relative humidity - or - overwatering. This can lead to nutrients deficiencies, too much heat and too much water will dramatically change the way plants handle nutrient and light. You probably need to reinforce your airflow, and try to follow a dry/wet cycle. Roots need to be on a dry/wet cycle to properly spread, searching for water. Now, your pH might be related too, a 7.0 pH is neutral whereas cannabis plants in soil need a slightly acidic pH range (6.0~6.5). Finally, we're missing a few informations to refine the diagnosis: what medium are you using (EC/PPM levels)? Have you been giving any kind of nutrients? If so, at what frequency? How often do you water, how often do yo feed, what's the volume of your waterings, how long do you let the medium dry between two waterings? If you look at all the hypothetical sources for this issue, I'm confident your baby will recover and become a strong adult. If you're stuck with yellowing+wavy leaves in a few days, keep us up-to-date and we'll be around to help. Happy growing 👊