Found a great video on the subject.
Another self watering grower, so there's quite a few I've found on youtube by now!
The reason I link this specific video is because it answers so many questions I've had about fertilizing and she has confirmed that 100-300ppm is the right level and explains in the best detail when to feed what. (species vs hybrids, root thickness, size of plant, growing season etc)
It's briliant, it's exactly the video I was hoping to find so here it is people: