Killer fish

[punkieg0]

I think I either have a cursed tank or a killer in my tank.
Currently have 2 clownfish, 1 diamond goby, 2 pajama cardinals & 1 filefish.

Tonight I found my 1 month old valentine puffer floating on the top. He was fine this afternoon. I have had 2 bi-color blennies and a fairy wrass all go missing over the last 3 months. Funny enough my current stock is my original stock that I started this tank with.
75 gallon
Running since January
Dish have been in since April with the exception of my Puffer.
Do any of these fish have a hidden aggressive streak? They all seemed to get along fine.

 

[motortrendz]

Have you tested the water? Parameters may be off. And it happens while the other fish were in there and they adjusted to whatever is off. But the new inhabitants cant make the sharp adjustment.

 

[HOOPDEEZ]

I would test for ammonia, the additional food waste from the puffer could have overwhelmed the bacteria.