Slush, I'm pretty sure, merge mines altcoins.  So if you were mining only through slush than that could explain it.  Or if you are mining through Nicehash to slush then your hash rate gets redirected by renters which usually mine new altcoins for brief periods.  If you have questions about how Slush operates then you should be asking in that thread.

If you want to mine here don't expect to be finding 17 Bitcoin Blocks in 2 weeks with 220Ths.  This pool is a great solution for a backup pool.  Maybe try using the main ck pool with this solo pool as a backup.