Qlik caches all calculations made up to a set maximum percentage of your RAM.
Even if you close all application and wait till the end of time, this caching will stay in your RAM. This is perfectly normal and the way that Qlik is designed. This caching will result in faster performance when someone starts asking the same questions again.
This should never be a problem, as you either
A) install Qlik software on a dedicated server
B) adjusted the maximum percentage of RAM it is allowed to eat up.
If RAM consumption is about 70% for your 128gb RAM machine, there is something to solve. Either your data model could use some improvements or the amount of data you load in your application is WAY to much for the memory you have (but we would be talking about billions of rows / many, many columns).