Gentian violet (Triarylmethane dye) used as a histological stain is known to possess antibacterial and antifungal properties. This antifungal property found in gentian violet aids in inhibiting fungal attacks in broiler diets (starter, grower and finisher diets).
Copper sulfate is used as antifungal in agriculture - horticulture, even in organic agriculture, to protect plants against some pathogenic fungi (Plasmopara viticola etc), in solution 0,5-1%. So it may be fungistatic for some pathogenic fungi contaminating fodder, but undoubtly a concentration of 0,5-1% in the diet have harmfull effects on poultry, even if they are much more resistant to copper than ruminants or other mammals
Copper - although still widely used in organic farming - should not be part of the treatment of choice in agriculture due to its persistent characteristics and adverse effects in nature. Therefore is was banned already many years ago as a feed additive in the EU.
Attached a link to a paper on gentian violet by one of the most important scientists on mycotoxins in poultry Dr Pat Hamilton.