Northern Lights with yellow tips. I suspected nute burn so I flushed. Did I do the right thing?

flushing is more for extreme situations. Runoff pH is not representative of soil pH, so unless you have a baseline of "normal" it's hard to assess. in this case if it was a couple parts of nutes that were too high, a flush also reduces the parts that were doing fine. It's better to reduce the provision of what you think is the problem rather than diluting the entire substrate. You mave have had too much P, tough to tell at this point in progression. this tends to display chlorosis in new grwoth but also thinner blades that i don't see here. The tip burn does align with p-tox. Unfortunately, more than one thing is possible and without more infor on how you feed and history of how you fed, it's more of a guessing game than it has to be. This is also less clear if it's a soil vs soislless/hydro grow. Keeping track is still useful for soil grows but not as precise of information. 7 weeks into vege.. expect that plant to double in size after flip. NL is a bushier plant, usually, so it won't be a 3x stretcher. you may want to flip as soon as you figure out what is going on. last thought -- are lights too close? i don't think so, but if top few nodes are extra tight, could be cause of some paling on top leaves due to a bit too much light. this doesn't account for the tip burn, though.