Hi Pal,
I'm using PK13/14 from Canna. This stuff is highly concentrated (so is PK13/14 from Plagron), so take care on how much you give your damsels.
I only give it, when I mention that the buds are too fluffy, or I see any deficites.
Suggestion from the producer is 1,5ml/l, I give max. 3/4 of that, once a week.
I gave it to my White Widow to ignite bloom because she was stunt due to PH stress.
You can easily overfed your damsels with this stuff.
If you're using any bloom fert., or Booster, don't forget that they have also a high percentage of P and K. It's adding up! Hooe this helps a bit