Chemi Pure Blue 5.5 oz Bulk - 6 Pack Each Single Unit Treats 35-50 Gallons

I have an 80g and using 3 bags. Is there any estimate on how long I have before I need to change them?

I have a 20g nano, would it be better to just put one of these or multiple of the nano ones?

I have a 75 gallon tank with an fx6 how many bags should I put in the fx6 at a time, one bag a month?

Can I use with a ammonia remover insert in my filter?