slight leaf burn and discolouration

hello humans,

i started my plant about 5 weeks ago.

its grown from a seed that was lying around.
the soil is left overs from a mix that i used to grow basil and bay (quite effectively).
i'm growing it outside, in a pot of about 30cm diameter, about 35cm high. there are also some other herbs growing in the pot (basil, thyme, oreganum).
it gets light sun from 8 to 12 and then full sun from 12 to 7.30 or so.
i water it once in two or three days, with tap water that humans are able to drink.
i fed it some organic fertilizer about 3 nodes in (about 5 days), but after reading it was bad i flushed the plant.
i noticed about 1.5 weeks in that some earthworms had decided to grow spontaneously. did some reading about this, and i believe it is good, so i've been letting them do their thing.
we are between spring and summer where i live.

now to the problem. i've noticed from the very beginning that the leaves are not uniform darkish green, but darker on the outsides and light green around the leaf veins/new leaf material. also, there was one leaf that always had a light spot about the size of 7 grains of sugar. the leaves have also always been quite dry and papery, with slightly lighter green specks all over. recently, a couple of the leaves started developing small burn marks (no change in external variables, except maybe watering patterns and the weather). it is always around the outside of the leaves. one small end leaf of the 2nd set of fronds is particularly bad, with the leaf curling up and completely dead. once i watered it, it seemed to slow down a bit, and it didn't get any worse.

any ideas as to what i should do about this? or if i should even be worrying? the plant is growing extremely well and quickly. it was planted after the other herbs and is dwarfing them at this stage. i will try to take some pictures, but i think i've explained the problem adequately. hope that anyone can help! i'm really enjoying this little organic growth experience and i would love for it to end in some kind of useful yield and not be a fail.