I cant see any bugs? The black specs just look like algae/silt but the pictures aren't really clear enough to see, it maybe looks like a bug in the 5th pic but can't ID it without more detail
Insects aren't normally a problem for submersed plants in aquariums, if there was any in there, they should quickly be eaten by fish. Do you have any fish in the tank?
Holes in the leaves like that could be a potassium deficiency, especially as you are in Edinburgh (like me), we have soft tap water and this is usually the first deficiency my plants show. Are you fertilising this tank, and what with? CO2/lighting?