Question about pg_xlog

Hi everyone,

I'm new to Postgresql and have a test environment with Postgresql 9.4.5
running on Linux.
Today I noticed that the pg_xlog was filled up to 18 Gb.
I have:
- wal_level=hot_standby
- wal_keep_segments = 100
- hot_standby = on
archive_mode = on

It's a test environment en I did a pg_resetxlogs() on the 6th of April.
I know that I shouldn't use this, and that it's only a last resort.
When I look in de pg_xlog directory I see xlog files that are kept sinds
that time.
When i look at the archive_status directory I see that all of the files
have the suffix of .done.
All the other xlogs from the time before the resetlogs are cleaned up as I
expected.
But I don't understand why the other xlogs aren't recycled.

I am looking for ways to find out why my pg_xlog is filling up.
- I checked the alertlog of the postgresql instance --> no errors
- I checked the WAL file location to see if the xlogs are being archived
--> they are present

Are there more ways to find out why my pg_xlog is filling up?
Is the pg_resetxlogs the reason why the older xlogs are not recycled?

I Hope that someone can help me.
Thanks in advance.
Regards,
Mariane