Dude you are absolutely NOT supposed to use Hygrozyme in a DWC Res.
My method: and I have Zero issues with slime:
The foundation: A Chiller. I know this investment is not cost effective for most, but know this: chilled water holds a higher DO( dissolved 02 content) than ambient growroom temperature water. This means that your plants will experience substantially more vigor and explosive growth than room temp reservoirs, and bacteria basically don't stand a chance at colonizing. Chilled for the Win. All other DWC methods are inferior without a chiller. Period.
H202 at 1mL per Litre every couple days. I should note that I simply add this step by default, and have never not used H202 in DWC. I'm of the persuasion that, since my recirculating system is chilled, the H202 isn't necessary, but I have no issues so it remains in the regimen. If it ain't broke..
Water changes. I do a 20% total volume water change weekly.
This routine, in part, stems from another hobby of mine: saltwater aquaria. Water changes and chilled water are a must in that world, and I find them to be pertinent in DWC. The hobbies are very similar, although aquaria is light years ahead of the grow world on water quality techniques and lighting especially.
Good luck.