I don't ph test never have. I haven't fed any nutes yet and it's only been potted 6 days like the Exo beside it so I don't get how that could happen. The Exo is fine and doubled in size,
Also the last glue cut that I've got in flower now went into the same type of soil straight from rooted clone and it grew fine with no issues.
"I don't ph test never have" - That'll be why the PH is too low (very low PH is obvious by the purple striped stems), low PH locks out Calcium and Magnesium at the same time but Magnesium defs take hold sooner.
The big magnesium deficiency is obvious from the yellow striped leaves where the chlorophyll is being stripped from the leaf margins.
Calcium deficiency symptoms will soon show if the low PH is not sorted.
"I haven't fed any nutes yet and it's only been potted 6 days like the Exo beside it so I don't get how that could happen." - Then either the plant was over fed with Nitrogen at some point before cut was taken or the soil the cut is in is too hot. Most likely (given the only 6 days) the cut came from a plant with too much Nitrogen in it.
"The Exo is fine and doubled in size" - That's irrelevant, the Exo is a different plant in a different pot.
"Also the last glue cut that I've got in flower now went into the same type of soil straight from rooted clone and it grew fine with no issues" - Same as above, different plant in a different pot.