The mottled lightness, it will manifest as a mag def, and more light will really make it pop. Look at the second node from top, the fan leaf.
That's just the crappy blurple lighting. Let's see them under normal light
@Zakfred. All sorts of threads here bitching about nOObs posting blurple or yellow pix asking about problems with their plants. A 5000K LED bulb casts nearly perfectly balanced light to be able to observe all the nuances of deficiencies etc to those of us that know what to look for like
@Renfro does.
Most 'deficiencies' in young plants are not. If anything maybe the pH is too high and some things are having trouble being absorbed. As the plant is trying to grow rapidly with still not a lot of roots it runs out of stuff it needs that are within it's reach so supposed N or Mg deficiencies seem to be happening. What is happening is those nutes are mobile and can be relocated to the rapidly growing tops that need it more. The plant 'steals' them from the old leaves first so they begin to show signs of deficiencies. Then nOObs toss all sorts of crap at their plants and kill them with kindness.
A lot more plants die from too much TLC than die from neglect.
Mobile nutes are N, P, K, Mg and Zn. Everything else is immobile and once in a leaf or other plant tissue is unavailable for further growth. When the immobile ones are lacking you will see problems with the newer growth in the tops. Mostly that is caused by the pH being too high as most of them other than Ca are needed in such small amounts that an actual lack of them in the root zone is very rare.
Speaking of Ca when I see someone post that spots on fan leaves are needing CalMag I have to laugh. Low Ca shows up first on new or mid-growth leaves as it's immobile and if it's not in the root zone then the plant will start showing deficiencies. CalMag is not the magic bullet as many seem to think it is. As low Mg becomes advanced brown spots appear on affected leaves.
Here's a great deficiency/excess pictorial chart. When you think you have a particular problem look real close at the clues around each particular nutrient. Waht you think may be your problem could be something else entirely. Most of what I've seen in the last 12 years in forums is pH/water related. If you use hard tap water your pH is going to go off scale upwards and mixing your nutes to 6.0 isn't going to do squat about that. Minerals in your water build up and you'd need to feed at pH4 forever to change it.
Save this chart for future reference.