Help - Fish dying off

[dough]

Over the last few days, all but one of my fish have died off. This was before and after a large water change with the same salt mix. The die off included new fish and fish that I have had for years including hardy fish such as clown fish. No sign of ich, or velvet patches. The remaining gobie has some dark spots on it. No changes in food that I feed etc.

Corals seem unaffected by this. All my corals look healthy. The peppermint shrimp are okay as well as my snails.

Over 20 years of keeping a tank this has never ever happened to me.

pH is 8.10

Salinity 1.028 which is high but not fatally high.


Any thoughts on what I should to do to start diagnosing this?

 

[Crabs McJones]

My best guess is some sort of parasite. Did it happen after adding a new fish? What are the rest of your water parameters? (Ammonia, nitrite, nitrate, ect...)

 

[dough]

My best guess is some sort of parasite. Did it happen after adding a new fish? What are the rest of your water parameters? (Ammonia, nitrite, nitrate, ect...)

The last fish added was a small tang from LA a few weeks ago so yes. Normally don't check the some of those parameters so I need to get over the LFS to get those checked.

I'm thinking parasite as well. Just stumped.

 

[Crabs McJones]

The last fish added was a small tang from LA a few weeks ago so yes. Normally don't check the some of those parameters so I need to get over the LFS to get those checked.

I'm thinking parasite as well. Just stumped.

If it moved through your fish that fast velvet would be my first assumption. Any pics of the remaining fish?

 

[dough]

If it moved through your fish that fast velvet would be my first assumption. Any pics of the remaining fish?

See below