Under most circumstances, you should have a feeding regimen in place for flowering. If you mix your own soil, adding all the amendments yourself then this isn't always necessary, but if you're not then you need to be supplementing the phosphorus and potassium that your plant is leeching from the leaves. It looks like it could be a really bad case of phosphorus deficiency, so you might want to consider using your bloom fertilizer on the plants that are just starting to show symptoms. Only start out at about 1/4 of the recommended dosage, especially if you're using a strong fertilizer that's made for tomatoes or perennials, and work your way up gradually.
Mr. Clandestine Reviewed by Mr. Clandestine on . FINNALY!!! My troubleshooting form is filled!!! HELP! S=Traditional Soil E-indoor E-Soil E-Plain Soil Mix CSL-Soil with Wormcasts (18%) + 80 soil + 2% rice E-Tapwater E-6.9 Water pH HRT-Source water EC (if hydro) E-2.5 months E-No fertilizer, yet. I used some N while they were vegging Rating: 5