Brakes going to the floor is due to air in the system/ Air is compressible, hydraulic fluid is not. I would have your brakes power bled at Brak-o or a similar nation wide brake repair shop. If you think you have a bad master cylinder perhaps you woulf want to buy this tool that cost as much as a professional power bleed, but you can do it yourself as many times as you want in the future for one purchase price.
Air is entering your system. It could come from a leaking line (rust through), a bad bleeder on a wheel cylinder, a bad wheel cylinder seal, or a bad master cylinder seal.