Hi emdub27. You’re a big reason I just joined this forum. You’re a wealth of information. I always look for what you post. So I figured this would be a good first post for me on this site.
It’s funny timing for this talk about Paul Cockson and others’ claims about boron in those two Canna Business Times articles. They definitely meant to write 0.875 to 1.0 ppm, not 8.75 to 10 ppm. I happen to have emailed him about their typo a few days ago.You’re correct that in their paper you mentioned they used 45 µM (0.4865 ppm) boron as the control. They induced boron toxicity at 10-times the control (4.865 mg/L or 450 µM).
For manganese, in that same paper, they also induced Mn toxicity at 10-times the Mn control. The Mn control was 18 µM (0.9889 ppm), so the induced toxicity level was 9.889 ppm (180 µM). So your use of 3 ppm Mn doesn’t sound too high to me.
There could be B and Mn toxicity at below 10-times the control.
In rockwool with CO2 and >1200 PPFD from Fluence LEDs with crop steering, I currently use 0.875 ppm B and 0.75 ppm Mn. But after reading that you run Mn at 3 ppm, and to get my Fe:Mn ratio to 2:1, I may increase my Mn to 1.875. I run Fe at 3.65 ppm with a 50/50 mix of DTPA/EDDHA (with 5.2% O-O) because I use inline UV for microbial control.
What do you prefer for Fe:Mn ratio? And what is your irrigation and substrate pH? I run pH lower than is typical for rockwool, so I am concerned about Mn toxicity from increased uptake.