Everything looking terrible! Help!

[derf]

Right now, almost everything in my tank is probably dying. My yellow tang is hyperventilating and staying near the surface, my mandarin is hyperventilating and staying in one corner, my chromis's are hiding and also hyperventilating, my goby is completely fine, one longnose hawkfish died about half an hour ago, the other is staying in one spot and also hyperventilating, one maroon clown is hyperventilating at the top of the tank, the other at the bottom, my cardinalfish are fine, all inverts and corals are fine as well. I checked salinity and I'm going to do water tests on everything. Salinity and temp are fine, and I added an airstone to the tank. Does anyone know what is happening and what I can do to solve??
Update: Chromis's are starting to come out, mandarin is moving, and the tang is looking better. Both clowns are still horrible and the ahwk is in the same spot. Wow, possibly two tank failures in a week after my quarantine crashed when I was on vacation last week. RIP SFE and Longnose Hawk. SFE was in quarantine.

 

[coraljunky]

post test results!

 

[derf]

Specific Gravity: 1.026
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: Not sure, my nitrate tests are messed up.
Ph: 8.2
Things are starting to look better, chromis's, mandarin, and goby are eating now. Hawk just moved to usual spot as well as one clown.

 

[coraljunky]

Did it look like they may have been fighting?

 

[sepulatian]

Originally Posted by derf
Specific Gravity: 1.026
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: Not sure, my nitrate tests are messed up.
Ph: 8.2
Things are starting to look better, chromis's, mandarin, and goby are eating now. Hawk just moved to usual spot as well as one clown.
What happened? Fish don't just turn belly up or start mouthing at the surface for no reason. Could you shed a little more light on the situation?

 

[derf]

Okay, the problem is solved. Was just a oxygen shortage. 2 fish died.

 

[beth]

Any chance that an inappropriate chemical was dumped into the tank? What do you have for water circulation, including skimmer, pumps, etc.?
Have you cleaned anything lately?

 

[derf]

I cleaned the filter intake and outflow today, that could have done something, and I don't think there could have been some chemical, as the only things I put in the tank that were liquids was marine snow. As for water circulation, I have 2 pumps, not sure what the gallons per hour is but there is a lot of water flow. For the protein skimmer, there isn't one set up now as the o-ring was leaking and I was waiting for a new to to be delivered. It should be set up this weekend.