Lucas Forumula: What ppm? Problems

[Adult_Toke]

My plants are about 3 weeks into veg. Unfortunately, they have been showing signs of what I believe to be magnesium deficiency, with fading/rust color patches developing between the veins and spreading outwards. It has become a particular problem within the last 3 days. Here are some pictures:









Two white widow on the left, and northern lights on the right. Both from nirvana. The first and third pictures most accurately captured the overall color of the plants.

In response to this, I upped the nutrient solution in my reservoir (DWC grow) to ~1000 ppm from ~600. Ph is at 5.8 The grow book by Jorge Cervantes recommends 800-1200 ppm nutrient concentration. Is this also appropriate with the Lucas formula, or am I still under-feeding my plants?

This is my first hydro grow and it has been going fantastic up until now. I really want to get things back on track.

Thanks for any advice.