New growth looks fine. Sometimes those first leaves have that type of blemish.
The only question i'd ask is: are you allowing top 1" to dry before irrigating or fertilizing routines? Always get ~20% runoff when you do. This will eliminate most possible substrate-related causes of such blemishes. Give a little scope under the leaves if anxious and look for small pests. Again, the wet-dry cycle of the top 1" will help prevent many potential pests too.