Is this Nute burn or something else?

Okay I've been using MG since I determined they were big enough it wouldn't kill them. Once a week only and provided it doesn't rain a couple days before. It rained a bunch last week so I waited. 2 hot dry days came through, soil felt dry, so MG went in. This plant is the only one suffering like this. This leaf is in the middle of the plant but this seems to effect leaves all over. Most of the leaves seem unaffected, which strikes me as weird. If it was nute burn wouldn't all the leaves look like this?


Edit: This is an outdoor grow. Around 3 months old. Soil in 5 gallon buckets.

Spider mites?

Nope, that's not nute burn. As clear as the pictures are I wish they were a bit clearer and at least one of the entire plant but still close enough to see the spotting and its location on the plant, as in lower portion or upper portion of the plant.

The spotting looks like it could possibly be caused by 'critters' on the underside of the leaves. If not then the problem would likely be caused by either a potassium deficiency if the spotting is on the lower leaves or a manganese deficiency if the spotting is on the upper leaves. Then again it could be nute lockout and one or the other is just the first element to be lacking in sufficient amounts so the initial symptoms could be deceiving so check your pH level to be sure.

cal mag.......

I double checked just to be sure. I don't see any black specks under the leaves. Wouldn't spider mites also effect the other plants? The buckets are almost touching most of the time. Also even outdoors I haven't notices any web strings on or near my plants. Isn't that a common sign of spider mites?