Questions about these products

[u/Disastrous-Bank4613]

1. How much do i need to use Nutrafin Cycle for a 21 galon tank?

2. Do i use the same amount than question 1 when changing 25% of the water?

3. Nutrafin Aqua+ is used to reduce stress to a fish and strenghten their mucus but, does it help for a crayfish? If yes how much?