Thanks a lot! 
seafire:~ # df -h /
Filesystem Size Used Avail Use% Mounted on
**/dev/sda6 19G 15G 3.3G 82% /**
seafire:~ # btrfs sub get-default /
ID 259 gen 7968 top level 258 path @/.snapshots/1/snapshot
seafire:~ # snapper delete 2
seafire:~ # snapper list
Type | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+--------------------------+------+---------+-----------------------+---------
single | 0 | | | root | | current |
single | 1 | | Mon Aug 7 16:07:50 2017 | root | | first root filesystem |
seafire:~ # df -h /
Filesystem Size Used Avail Use% Mounted on
**/dev/sda6 19G 9.8G 7.5G 57% /**
seafire:~ # /etc/cron.weekly/btrfs-balance
Before balance of /
Data, single: total=15.01GiB, used=9.27GiB
System, DUP: total=32.00MiB, used=16.00KiB
Metadata, DUP: total=640.00MiB, used=236.41MiB
GlobalReserve, single: total=27.02MiB, used=0.00B
Filesystem Size Used Avail Use% Mounted on
/dev/sda6 20G 11G 8.0G 57% /
Done, had to relocate 0 out of 22 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=1
Done, had to relocate 0 out of 22 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=5
Done, had to relocate 0 out of 22 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=10
Done, had to relocate 1 out of 22 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=20
Done, had to relocate 1 out of 21 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=30
Done, had to relocate 0 out of 20 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=40
Done, had to relocate 2 out of 20 chunks
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=50
Done, had to relocate 0 out of 18 chunks
Done, had to relocate 0 out of 18 chunks
Dumping filters: flags 0x6, state 0x0, force is off
METADATA (flags 0x2): balancing, usage=1
SYSTEM (flags 0x2): balancing, usage=1
Done, had to relocate 1 out of 18 chunks
Dumping filters: flags 0x6, state 0x0, force is off
METADATA (flags 0x2): balancing, usage=5
SYSTEM (flags 0x2): balancing, usage=5
Done, had to relocate 1 out of 18 chunks
Dumping filters: flags 0x6, state 0x0, force is off
METADATA (flags 0x2): balancing, usage=10
SYSTEM (flags 0x2): balancing, usage=10
Done, had to relocate 1 out of 18 chunks
Dumping filters: flags 0x6, state 0x0, force is off
METADATA (flags 0x2): balancing, usage=20
SYSTEM (flags 0x2): balancing, usage=20
Done, had to relocate 2 out of 18 chunks
Dumping filters: flags 0x6, state 0x0, force is off
METADATA (flags 0x2): balancing, usage=30
SYSTEM (flags 0x2): balancing, usage=30
Done, had to relocate 3 out of 17 chunks
After balance of /
Data, single: total=11.01GiB, used=9.27GiB
System, DUP: total=32.00MiB, used=16.00KiB
Metadata, DUP: total=384.00MiB, used=235.02MiB
GlobalReserve, single: total=25.62MiB, used=0.00B
Filesystem Size Used Avail Use% Mounted on
**/dev/sda6 20G 11G 8.6G 56% /**