Does it wipe off? It looks like a little bit of BBA. You might try dosing some excel to it.
Sorry should of said!For the deficiency part, there are some other things that needs to be addressed to pinpoint the problem.
Does the problem only affect one leaf or the entire plant, or several plant? (if its entire plant or several plant, then may be some kind of deficiency)
what kind of substrate are you using? (If it is a rich substrate, then most probably micros will not be the problem)
Do you have low, medium or high light? (this will give clue on fert consumption)
Any CO2 injection(DIY/pressurized/none)? (with combination of lighting and fert dosing info will give clue on problem)
How long have the plant been in the tank? (this part tells you that the plant may be melting from transplant or trying to convert from emersed to submersed form, BBA from tank it came from, etc.)