Hi everyone.
This is my first real year in bonsais. My trees made it through winter and now with the growth seasons I can finally see leaves.
But after some time here is what happened to the leaves

Oak:



Maple:


It looks like the leaves burnt. They are "full sun" oriented from 7am to 2pm. I fertilize them with a 5/5.5/7 every 2 weeks.

Do you have any idea what it could be?
Thank you!

The bottom plant is a Sycamore. Not enough water is the usual cause of leaf "burn" the oak looks fine.

Thank you @m5eaygeoff !