You won't need much coolant I have a small pump a radiator and 12 metres of pipe work. In all it runs on just over half a litre....even after 2 hours of running the water temp is only 18c. After the install i had small bubbles for 1 hour max since then i have had no bubbles or lost fluid in 7 months. You will be fine. I bet most if not all of your bubbles are coming from the mains tap water. When you do get it all sorted out use pc cooling fluid as tap water in parts of our country can be very hard. You don't want your spindle to scale up. Maybe the water is soft where you are. Cheers Andrew