leaves start to be yellow this morning :-(

There's a few things that could have caused this. I'll do my best to help you with no info except the above to go on. 1 fans like this.can be caused by being too close to a circulating fan and/or a heater. 2. Like the others said, maybe you spilt some nutrients on her but that wouldn't look exactly like this.... 3. Its a problem with your ph levels causing nutrient lockout. And I would be worried about that, actually because if it continues it will just get worse. 4. If your ph levels are fine, then you are feeding too much and she's trying to expel what she doesn't need (which is why nute burn always happens in the leaf tips first). It is not light burn. It is not likely a spillage of liquid. It is likely to be wind damage or. Slight nutrient overdose or imbalance of npk ratio or ph levels would be my best guess.

It's nutrient burn feed it water only for a week then go easy when introducing nutrients again

Did you spill something or touched leaves with something ,nutes or water? Doesn’t look like a deficiency to me .more like nutes burn .anyway plant look good 👍🏼

your plants looking healthy, mine did the same thing and some water was spilled on them. If it was nutrient burn you wuld expect more of the tips to be effected not just one part of one leaf. If it was light burn you would also expected a more rounded out effect vs one section on a lower node vs the upper most growth. Keep going and Happy Growing!

Looks like either nutrient or light burn or you may have accidentally spilt something on the leaves ? It is not a deficiency