Hydroguard is way diluted compared to Southern AG garden friendly fungicide. They both contain bacillus amyloliquefaciens. Southern AG is 98% concentrated if I remember correctly and people have great results with that.
I'm on the sterile route though with regular bleach(sodium hypochlorite). 3-5ppm is recommended for DWC. Here's the dilution calculator:
Chlorine dilution calculator
Oxidizers are easier to use without a chiller IMO but people have success with Southern AG without it. Bigger water volumes and keeping the reservoir outside of the grow space helps to keep temps down.