Hi and thanks for using 2carpros.com.
If the fluid is disappearing, you have a leak. What I need you to do is first inspect under the vehicle for wet areas. Check along the frame and at each wheel. Also, here is a link that discusses possible causes for the pedal going to the floor:
If you have a helper, fill the master cylinder with brake fluid and have the helper pump the brakes while you check under the vehicle for leaks. If you live in an area where there are things that can cause corrosion such as salt on the roads during winter, there is a very good chance one of the steel brake lines has rusted through.
Let me know if I can help of if you have other questions.
Saturday, December 15th, 2018 AT 9:47 PM