The dark green leaves may be a tad bit too much nitrogen (some slight clawing is visible), not sure if he's adding it or not, however that wouldn't affect magnesium uptake. The burnt tips can be many things, zinc is a possibility. If the plant is short on magnesium, it cant uptake phosphorus properly (purple petioles), leaving it behind in the medium, too much phosphorus would lock zinc out first, which would create burnt tips. The possibilities are many, but the intervenial yellowing, looking at the other leaves, is missing magnesium, that's what i can say. Again, if OP needed a more accurate response, then more info should have been added, i can only comment on the info given and pics posted. Being this late in the grow, im not even sure much is necessary as magnesium deficiencies show their signs weeks after it starts..by now, with such little time left, maybe it's best to let her finish..still many viable leaves left to get her nutes for the end. Yes, nitrogen should be cut out by now.
op said there are more.