Iveco 75E15 braking system not building pressure ?

I have just bought a 75E15 Iveco truck, the braking system was fine and working, but after getting her home I noticed there was a 3rd bottle on top of the pressure tanks that was empty, it looked like it had been empty for year. Antifreeze was listed on the bottles lid and inside was a lot of dry limescale, which would tie in with there being water in there, so I added 50 parts water and 50 parts antifreexe. Thing is ever since then my braking system want build pressure past 4bar and the emergency needle doesnt build at all ?

Does anyone know what I have done or why my Iveco braking system is now not pressurising ?