I need help in identifying the problem here. There are these blackish , greyish coloring showing up along the edges of the leaf's. These are clones in a greenhouse. Clones are in new soil that was bought in bulk at a local reputable landscaping gardening center. The clones have been in the soil for about 3 weeks. Recently we experienced some very cold temps, around 28 degrees Fahrenheit for 2-3 days which i thought was causing this issue but im not sure. I use Athena nutrients and use them as the product recommends. This strain is called sherbcake, i have other strains in the greenhouse that are not showing signs of anything like these are. I also did an IPM spray of DR Zymes recently as well as Lost coast plant therapy. As far as other variables, i fill my tanks with water and PH the water and ferts to 5.8 to 6.2 . My EC on ferts is 3.0 and PPM is 1500 as recommended by Athena. I would like to know what others think about this so i can correct it. Thank you very much