Cm would be my guess not knowing your feed mix?Probably not a pH issue since my soil is pH adjusted. Honestly it looks like the brink of a calcium and mag deficiency to me I think she's calling for more newts! It also could be that my scaling worth of shit and I can either be giving them two less or too much so I might go back to the old teaspoon method
Where is it appearing on her bottom leaves?
Stay safe
Bill284