So here's my experience with one of my runs last year (yup old thread lol). I decided to run spray nozzles in my trays instead of flood and drain, thinking more air, less issues... nope lol. Second week of lights on the rot hit and hit hard, one plants had it so bad it had one brown root strand left. I threw some 35% at it at, forget the ratio but it was probably .25-35 ml per litre, didn't touch it, added bleach at about the same mixture, the bleach helped turn the roots white but they were still struggling so I tried hydroguard, I did also start chilling the water so it may not have been the guard but my roots recovered, the plants recovered, by the end of the grow I had a root mat 4-5" thick covering my tray. Yup, can't buy it here, Not approved for sale in Canada, I honestly believe it's the best thing I have ever used for root health, trying to find a replacement so open to suggestions as well.