I'm not sure about Diamond Nectar, I just use the base GH 3-part. One other thing I'm noticing is that the lightening looks like it might be from the lights being close...that sort of blotchy white pattern seems like it's more related to the light than something that's wrong in the root zone. Before you add any additives to the root zone, I'd consider your leaf temperatures. If your room temps are in the 60's, you're probably not in the ideal part of the vapor-pressure-deficit curve for that much light intensity, so what could be happening is an acute Mg deficiency only in those parts of the leaves that are most proximal to your light source, which is robust and close given your first post.
My point is that treating this issue in the root zone might do nothing, or create a further imbalance. Something about really high levels of light with low leaf temperatures seems to cause this bleaching effect closest to the lights, and it seems like it's become more prevalent with LED that don't throw off the huge amount of warmth that HID lights like HPS do.
There's a grower on another forum that has an absolute NASA-like grow setup, and he swears by 65%+ humidity and 82* F leaf temps. That sometimes means running a room around 85* since the leaves often get a ton of air movement from circulating fans in a controlled setup. The idea here is that with 82-83*F leaf temps, the plants are able to metabolize everything from the root zone more appropriately in that high-intensity lighting zone. If you go down into the 60's, certain processes shut down that then create the deficiencies you're seeing. Given that your plants appear very healthy outside that max-intensity light cone area, I'd suggest pursuing a more idealized environment before increasing the concentration of fertilizers added to the roots.
This is really tricky for small setups, and can get complicated fast.
Personally, I struggle with this mightily. My environment is crazy arid, so I run a humidifier outside my tent 24/7 and keep my house about 3* warmer on the thermostat than I would prefer, and that still doesn't really address the issue when the lights go off. I try to aim for 78-82*F and 65% humidity, but right now my flowering cabinet runs about 65* lights off, sometimes single-digit humidity levels. That creates its own set of problems, and if you look at my blog entries, you can see the effects of that in the leaf discoloration. I will also say, finishing flowers in cold, super-dry environments seems to create some of the frostiest, most potent weed I've ever seen, like, it's insane. It also cuts my yields by like 30-40%, so I really need to come up with a solution.
