How do I kill pathogens in the reservoir, BEFORE they hurt my plants?

1 cap for of bleach per gallon of water will kill pathogens in the reservoir. HOWEVER if you use organic nutrients/additives or any beneficial fungi or mycorrhizae the bleach will kill that to. Food grade peroxide is also used to stop disease & pathogens but there again peroxide will destroy all organic nutrients/additives or any beneficial fungi or mycorrhizae. As far as commercial water sanitation products 4 main ones come to mind. I will add more as customers feed back permits. These are not listed by any preference of Simply Hydroponics & Organics so I will list them alphabetically.

FloraShield is a combination of anti-microbial compounds that are active again many fungi & bacteria that cause plant disease. FloraShield Used as a general disinfectant for cleanup of tools & growing systems/containers as well as a nutrient reservoir treatment for root protection. Hydroguard is safe for use in soil as well as hydroponics. Hydroguard bio-fungicide water treatment solution colonizes plant root zones with a mixture of beneficial bacteria to strengthen & protect plants. Because it forms a barrier against damping-off disease & root rot. Hydroguard is especially effective when used with seedlings & cuttings. SM-90 is an effective treatment for fungal infestations that can be used as a soil drench or in a hydroponic solution to treat root diseases, molds, mildew, & leaf spot. When applied directly to the foliage, SM-90 also discourages many common pest including aphids, thrips, spider-mites & whiteflies. Additionally, SM-90 increases plant transpiration rates, resulting in increased metabolism & accelerated growth rates. Contains natural plant extracts & is non-toxic. Zone is chloramines derived product that kills all disease/pathogens giving your plants clean healthy roots. Zone will kill all Beneficial bacteria as well as bad bacteria. Zone works under the theory of having a completely sterile root zone.