I highly doubt it is the loaches, The do not eat plant material, but that shark does and if attempting to get at algae on the leaves it might be eating right through the leaves also. He is most active at night just before dawn, so try getting up before he does and be by the tank with no light on above but some window light in another room (just enough for you to see by) then wait. chances are you'll see the culprit gnawing at the leaves. Those holes in the pics have shapes like the leaves are being eaten by something going for the little areas of algae on the leaves. I have witnessed these sharks before and they do have an affinity for algae just before dawn.
Hope this helps.