Unfortuanlty I dont know of a product that can be added to the nutrient res tank
but u could use a foliar techniques "protector" advance nutrients
Protector is a foliar additive aimed at preventing and curing mildew outbreaks which can harm your fruits, flowers and foliage. Highly effective in early tests, Protector is a good product to have around should you ever start to get mildew problems.
another option (I HAVENT TRIED BUT GRANDAD HAS) is create a homebrew with milk :-
Preparing a Milk Solution and Spraying Schedule
The correct dilution and spraying schedule for garden plants depends on the situation and takes some trial and error.
A milk fungicide solution can range from 1 part milk to 9 parts water, to a strong, milk-only solution. A 1:1 dilution may work for a week, but a 1:8 solution requires spraying every 3 or 4 days. (DEPENDS WHAT STAGE YOUR AT)
Skim milk may work better than whole milk, as the higher fat milk may clog a sprayer; even reconstituted powdered milk works.
Uses for Milk Fungicide
Milk was originally used in the garden to treat powdery mildew on squash plants.
Milk has also been used to cure Botrytis. This was applied full strength.
Black spots and rust can be controlled but not cured with milk. Fortunately, milk can prevent the spread of these fungi to other plants and new leaves.
NB THESE ARE FOR FOLIAR APPLICATIONS>>>NOT TO BE ADDED TO RES
best of luck if u do find one let us know
welcome to THC