To really know what is going on with your feedings, we need to know what your PPM readings are on every feeding and what products were used. Time released salt-based fertilizers are easy to overfeed with because of the compounding effect and dangers of toxic salt build up in your root zone. Miracle Grow was mentioned and this is a time release salt based product. Some potting soils are mixed with slow release fertilizer. It all adds up.
They have the look of being a little over-watered which should purge the salts out of your soil, so I'm thinking toxic salt build up isn't your problem. But to my eye your plants look to have a nutrient lock out. Assuming you started with decent soil, it is NOT common to have a nutrient deficiency of your scale from under feeding. I've grown some plants in dirt and never given them a single feeding of anything but water and they did surprisingly well. Some strains are incredibly sensitive to nutrients and like very low levels.
So I understand that you don't think you are over-feeding them, and maybe you aren't, but stay open to the idea a little longer. Over feeding DOES often look like a nutrient deficiency. That 52P sounds crazy to me. You will soon learn that putting something on your plant simply because it is what you have around, is a very bad idea. Everything you put on your plant needs to be evaluated on a stand alone basis and within the context of everything else you have put in there. Get a good nutrient feeding schedule from an experienced grower with proven success at every stage of the game and copy what they do next time, including their dirt recipe. Tossing more and more product down to try and fix something is often a death spiral. With good dirt, less is more.
You have a picture of a burned leaf and you can see little white globules on it. Check these out with your microscope to confirm that they are not larva. I'm guessing they are minerals but you need to confirm this to rule out pests. Large fan leaves should start to look bad at this stage of the grow so don't take that as a sign that you necessarily need more nitrogen.