Need help and advices

[WeeTT]

I currently having problem with my green vegetable; I noticed that burn at the edge of the leaf and leaf crack.

Is that a nutrient deficiency or some sort of disease? I have put in 20g potassium nitrate and 20g calcium carbonate into the system but doesn't seem to improve.

I have a water volume of 1.0 m3 approximately. Is the amount of potassium and calcium put in is sufficient? 

 Appreciate some help and advice. 

[Alex Veidel]

Could you post a picture? Pictures are helpful when it comes to this kind of stuff.

[WeeTT]

[WeeTT]

Additional information my current pH is running at 6.4. Nitrate is less than 5ppm.