what are these marks on my leaf?

if you grasp the stem of that leaf right where it joins the main stem and pull down it should just snap off right at the joint.

...once you remove it take it out and flip it over and examine it very closely for pests, if you don't see any then just keep an eye on things and look for others.

...btw, it looks like the plant is hungry, can't tell for sure because your pic only really shows that one leaf but i see some light green leaves in the pic and that could indicate hunger.

peace, bozo

...oh yeah, pulling that one leaf off won't hurt anything.

Could something have dripped on it, maybe alcohol? Could you also show us the leaf your hand is covering?

Looks like you may have a mealybug problem.

It is one of three things... You dripped a little pH down onto a leaf and didn't notice it and it burned the spots or you dripped alittle water on there and it beaded up acted like a magnifer and burned the spots or the was another leaf over lap that and it got moved away and there was condesation there and it beaded up and burned the leaf.
It looks to me like a little drip of pH down I've done it myslef when I was in a hurry,. It not a disease or pests and its not going to spread unless yours really careless and start splashing shit all over.

Talk about excellent feedback op! I think you got your solution! Light green leaves beign green indicates hunger i need bozo to check out my pics then!

thanks for all the replies, I have no signs of pests what so ever and I wouldnt be surprised if a bit of nutes or ph down got on the leaf as its pretty low down. sort of feel bad for removing it now lol Poor leaf.

Oh and my hand is there to just raise the leaf. the yellowish leaf you can just about see under my hand was a past problem with magnesium def

What are your temps light on and off.