Clair database keeps on growing

Hi,

 My customer is questioning the storage on Quay 3.5.0:

The database for Clair (also version 3.5.0) keeps on growing. Last week the disksize of the database was increased from 100 GB to 250 GB. Today the Clair database was 224GB:
postgres=# SELECT pg_size_pretty( pg_database_size('clair') );
pg_size_pretty
----------------
224 GB
(1 row)

When does the behaviour occur? Frequency? Repeatedly? At certain times?
Last week the size increased from 100GB to 224GB. The usage is still the same as the months before