I'm not an expert but looking in my Jorge Cervantes book, it looks like a later stage of Potassium(k) deficiency?

If the yellowing started from the stem area and spread to the tips it could be a Iron (fe) deficiency

all of these deficiencies could be due to pH problems as the nutrients may not be properly took in by the plants

here's a ph Chart someone else posted elsewhere
Revanche21 Reviewed by Revanche21 on . Can you help Identify Alright. Well i can't tell if this is a problem or not, but i'm getting brown spots on some of the leaves that are starting to yellow. I'm in week 5 and i'm unsure if the leaves are already starting to drain themselves, a ph problem or an infestation. There are gnats that circle around the lights but i put up fly paper, kills alot of them. Anybody have an idea? Rating: 5