When you see leaves that point to deficiency, don't get all hasty or freak out and start giving it more nutes. Consider your plant's history first. Have you been feeding it every time you water? If so, consider a salt build up. Is it in hydro or soil, or coco or rockwool, etc. Soil, coco, rockwool all get salt build up easily. What were the PPM you fed it with? Did you feed it with organics, which is much harder to burn with? So, I saw a few leaves like this on on Northern Lights. You can see how the other leaves look normal, but that one on the left doesn't. Between the veins it is starting to yellow. This one looks like magnesium def, but, did it start from the top or edges? I can't tell from just one leaf, so I keep looking. I look at under leaves that don't get much light, if any. I find leaves like this. Now I can see that the yellowing starts from the top. I can also see some nute burn. A few leaves that looked totally healthy, had very little burnt tips. Now I am pretty positive it is nute burn, especially because I kept raising the nutes to see how much they could take. Last time I nuted was with 1200ppm. Also, I water with water and florakleen between each feeding, so after the plants completely dry out, I water with water and florakleen, then when they dry out again, I water with nutes. Anyway, I considered my plant's history before jumping to conclusions. If I fed them more nutes at this point, I could have stunted them. But how does a plant get nute deficiency if it has nute burn? Seems like a contradiction, huh? It's not. When you feed to many nutes, you cause salt build up, which in turn causes lockout. Lockout makes it so the plant cannot access the nutes, even though there are TONS there. I also looked for purpling in the stems because this is a sign of lockout. There was some. Like red/purple veins running along stems, and some leaf stems turning a bit purple. Not all of them, just some. This is caused by a build up of anthocyanin, which is caused by a deficiency of N and K. In this case, I pushed my grils too far, so now I know their vegging limits. Under 900ppm. Only feeding ever 3rd feeding instead of ever other feeding as I was doing. They are in Fox Farm Ocean Farm mixed with Fox Farm Warrior and lime. If they were in pure rockwool, I could easily get away with feeding 900ppm every other watering, as nutes drain from rockwool easier. It is a good idea to flush every two to three weeks. Here is how I corrected the problem. This is a bit based on experience and from Jorge Cervantes advice. First, my plants are in 3 gallon smart pots (fabric pots) with holes cut in the bottom. I poured 3 gallons of ph 5.8 water with 1tsp of Florakleen per gal into one Northern Light. Then I started pouring just pure Ph 5.8 water, no Florakleen. I did this until the run off was about 250-300 ppm. I was suprised at how high the run off was at first, which clearly told me there was a salt build up, and that I was on the right track for treatment. After first gallon, I got an error for run of, which most likely means the reading was too high, but I'm not sure how high my thing reads. I then poured galon 2 and 3 of florakleen water through, and got a run off reading of 1800 ppm. Wow. 3 gallons later, with Florakleen, and 1800ppm, when the most I fed it with was 1200ppm. No doubt, there is a salt build up. I started to flush with just ph water. The reason this took so long, is after I poured a gal through, I had to pump the water out of the run off tray, into a big pot, then test the water, then dump it. After the first gallon of ph water, 560ppm. Nice. Huge reduction. 2 gal, 400ppm. 3 gal, 300ppm. 4 gal 250ppm. I figured that was good enough. She should recover nicely. I noticed no more damaged leaves today, so as seems well. I repeated the same process for the second NL, until 300ppm. By this time, I was getting lazy, so I took the Mendo Purp, Lucy, and White Widow into the shower. I rensed each one for about 3 minutes, until a good 6-9 gallons went through. I watched until the run off looks pretty clear. I am not worried about the ph of my tap water. It was 7.1 at the time. I treated my soil with a good amount of lime, so the ph in the soil stays 7.0 really easy, same witht he coco that I treated with lime. This means when I water with 5.8ph, it shoots up to 7.0 within a few hours. I didn't test the run off of the other plants because I knew about how much water needed to go through them to get it down. This is one method recommended by Jorge Cervantes. After they dry out, I will feed them with Ph water 5.8, B1 plant starter--Lilly Miller UltraGreen. It provides cheleted iron, manganese, and zinc, and of course B1. This stuff is great for when you transplant, leech, flush, or put your plant through stress at all. I will also feed with Alaska Fish Fertilizer. 5-1-1. This is organic, so it is hard to burn the plant. I want to feed with this and just water a few times before feeding with flora series again. I want to be sure they are recovered and don't burn again. I will also feed with Hygrozyme or something similar, just in case the roots suffered at all. In fact, I might just water with water again when they dry out. I will water one with just a gallon of water and check the ppm. I don't want to cause more lockout. There is enough nutrients in the soil now and in the large leaves for the plant to pull from. I will add the B1 and Hygrozyme regardless, though.