If you make a solution 100 ml (1%) you need only 1g and only 6 drops (1ml ~ 20 drops). 50g are enought for years or about 10.000 old films…. 😉
You can use it for old paper also.
.
https://shop.es-drei.de/heterocyclen/295/1-2-3-benzotriazol-min.-99?number=123BTRIAZ0.05