All I can say is, I've seen it stop root rot in hydro in its tracks.
Sorry, a correction:
Hydroguard does not "kill detrimental bacteria in soil and hydro." It is bacteria that digests organic crude (with plant nutrients as a by-product), and is not going to kill anything. According to Botonicare, "Hydroguard® contains unique beneficial bacteria, Bacillus Amyloliquefaciens, selected specifically for its superior ability to enhance the symbiotic relationship between the roots and their surrounding medium."