Sudden Death

[Nashoda]

Hi everyone,
I am fairly new at my freshwater hobby,(and first time on forum) but i have 2 co-workers who are old hand at it and they have helped me a great deal. Although they have no idea what happened to one of my fish last night.
I have had a 30 gallon tank for a few months now, (my friend gave me his filter for bacteria to help with cycling)and my water is and has been perfect, ph 7 and 0 to everything else. Its a planted aquarium with Co2 and plants are doing excellent as well as my fish. One issue happened last night that I'm baffled about. I bought 3 angelfish 4 weeks ago, were in quarantine and they ate well, nothing unusual so in main tank now. Living really well with my other fish for weeks now. However, last night I was feeding them Brime shrimp like usual and 1 angel and then suddenly went crazy. Hit its head into the tank a few times, then did "flashing" behavior (think that's what its called when they rub their body against plants)then went up in a corner and just sat there. Five minutes later went to bottom of tank and sat there, then ten minutes later went to corner top of tank and sat still. By morning my poor angel had passed away.
Since I work in the veterinary industry I was able to have a microscopic exam done on the gills, and they appeared normal. Any ideas? Ever heard of such a sudden change? I am concerned for my other angels and the other fish as they are all a wonderful community. Some will be moving to my 55 gallon when they are bigger, so I don't want contamination as it will be a discus tank primarily and need perfect water.

Thank you, Nashoda

Tank size:30 gallon
pH:7
ammonia:0
nitrite:0
nitrate:0
kH:
gH:
tank temp:26

Fish Symptoms (include full description including lesion, color, location, fish behavior):above

Volume and Frequency of water changes:every other day 15 percent water change

Chemical Additives or Media in your tank:iron once a week

Tank inhabitants:molly, gourami, angelfish, clown pleco, zebra loach, cardinal tetra, cory's,many plants

Recent additions to your tank (living or decoration):dwarf gourami after in quarantine for 2 weeks

 

[Tolak]

Sometimes fish get spooked like that, and the results of hard collisions with the tank or objects can cause internal injury. As far as what spooked the individual & why it's hard to say. Most likely it was some sort of internal injury that caused such a quick death in an otherwise healthy fish. Sorry for your loss.

 

[FishFillet]

yes it does seam like your anglefish was spooked and injured itself internaly

 

[Nashoda]

Hmm, never thought of that. Even though it's a loss it is better than a possible virus or something. I worry with that angelfish virus they talk about.
Thank you , much appreciated