Yellowish Spots Appearing Fast

Basically earlier today my plant has started to develop small yellow spots on the higher leaves and larger brown spots/patches on the lower leaves. They are also drooping quite severely. I couldn't get a photo of the lower leaves but here are the top ones.

Only 1/4 of my plants has got these, and this is the only plant that I've given nutrients so far, because I was worried about exactly this happening..

So is it nute burn? Something else?

Should I flush it out or just leave it?

I stress that the lower leaves are getting quite bad, drooping A LOT, and generally look brown and awful

Over watering..just water less...then the leaves will be less brittle and not so spotty, and if you are feeding those seedlings, then stop.

Thing is it's only started today and on the one plant that I gave nutes. A couple of the leaves lower down literally look like they're about to fall off they're drooping so much, and look brown all over. The spots don't just look like colour either, they're more like craters, so I'm assuming it's nute burn.

Would it be a good idea to flush it?

I don't think it's overwatering because I water the other plants exactly the same amount and they're fine..