Looks like calcium is needed.
Now, Calmag is not meant to be used at such low dose!!
To address a deficiency start with 5ml per litre. Don't worry, CalMag is very gentle and won't burn your plant at this trenght.
But 0.3 ml per litre is a waste of time.
Just don't forget it will take a few days, a week, to start to see some results