HydroGuard and other root rot inoculants work by forming a live colony around the roots that out populates the bad microbes. I think the Hocl would kill off those colonies. I think we have had this conversation before? I personally would not use it.
If you are so worried about algae why don't you just stop the light from getting to the hydroton, this is possible even on a flood table?
You can, and I do use Great White, Mykos and other mycorrhizae inoculants in hydro. Usually just at transplant. You just apply it to the substrate. Sprinkle it on!
Off to bed..... Good Morfnoevight All!