plant care

Hi all, this plant is on day 18 and looked to be going strong up until this point however I am noticing growth that doesn't seem right. First image shows the issue and second and third image shows different plants under the exact same conditions and feed. Strain- velvet moon Age- currently...

Not everyone finds it necessary to check PH and some growers get lucky and never have to check it. But PH is essential for plant health and growth. I do not fall into the category of lucky. So, here is part of my story.