fish dying

Help fish are dying during night I'v lost 4 and clowns a cardinal
I first lost 2 clowns then replaced them
Then lost a cardinal yesterday and one today this was 4 weeks from previous death
All parameters are good
It's a 30g
With more than enough rock
I'm currently cycling a 130g
Live stock are
Goby chalk
Regal baby she's great
Cardinal and clowns
Do have some hermits and snails