Brabantia

A tsp = ~ 4gr ( P..ers 20-20-20 measured and weighed) 3/4tsp --- 3gr /3.75L ---> 0.8 gr/L at 20% N ---> 160 ppm N /2W ---> 80 ppmN...

Beautiful !

And how ppm or mgr/L nitrogen for full strenght ?

That's very imprecise information! All year round with a dilute solution, it could be once every 2 weeks with a solution containing 20...