Hi @X3NiTHOscillatoria uses N in the production of Anatoxin otherwise known as Very Fast Death Factor...
Many thanks for your input. I referred to the serious toxicity issue in post #3 above. When I discovered the term 'Very Fast Death Factor', I was gobsmacked! This seemed to be very relevant to what I'd witnessed with my GBRs and Panda Garras. There they all were one day - the epitome of health and about three days later, they were all dead. What could have happened? I could no longer afford to pay lip service to this thing called BGA.
I would welcome your further inputs in trying to remedy this problem. My background is in the field of electronics, not microbiology. I need all the help I can get. Please keep the suggestions coming.