Our systems are primarily designed to save money, improve efficiency and allow high density. Changing fluid or refilling is not necessary with well designed systems, because they are made to avoid or minimize losses (including vapor) or contamination. We found that spilling liquid while pouring in and out of containers is by far biggest source for losses, and we have integrated ways to avoid spills on initial filling, along with many other technical features that are designed to keep fluid in the tank.
The fluids are inert and have a shelf life of 30 years. There will be no significant degradation of the fluid when it is used for electronics cooling (in a recent study, scientists looked at fluid from servers after 23 months in use). We still have fluid that was first used over 20 years ago.