Fish suddenly dying

So I posted previously about being afraid to combine my tanks for fear of disturbing my yellow blotch rabbit fish. Well, I came home today and she was dead. Furthermore my yellow watchman goby is acting horrible. My paeans are right in line: ph8 (I know that's low but it's how the tank has always been) 0 ammonia, 0 nitrites, 0 nitrates, 0 phos, alk 8. What the heck is going on!?! All my other fish seem totally fine! As a reminder I have a lawnmower blenny, bicolor dottyback, fire fish, six line wrass, yellow tail damsel and of course the two mentioned above... well I guess one now... any ideas would be GREATLY appreciated!!! I wanted to combine the two tanks but now I'm afraid to harm my two platinum snowflake clowns........