As far as I know, Android doesn't support CalDAV or CardDAV. Any apps I tried were lacking in some way or another. How did you get Android to sync with Fruux?
I used DAVx5 from Bitfire (available on F-Droid and the Play Store) and it works very well. It is able to sync on multiple devices and from multiple providers.
I have been quite happy with https://dmfs.org/caldav/. There is also a carddav client from the same publisher.