The tomato sauce for sweet and sour fish is the same as that for bread and KFC. The shelf life of ketchup is 1 year, such a long shelf life.
There are so many ways to eat ketchup that French fries can be dipped in ketchup. You need ketchup to make pizza. You need ketchup to make spaghetti. You need ketchup to make lion's head. Too many usages ...
If you don't usually eat ketchup, if you really want to use ketchup, go to KFC or McDonald's and ask for several bags. You can also buy delicious food in small bags (as big as KFC ketchup).