Mandarin Dragonet death

[KeepSwimming12]

Hi this is my first post on an aquarium forum so I’ll do my best to provide as many details as possible. I bought a captive bred mandarin dragonet for my 20 gallon aquarium. He ate mysis and obviously loved copepods. I put copepods in the aquarium every day which I know is far from cost effective but I wanted to do the best I could for him. There were heaps in there and I watched him graze but the fact that he didn’t put a dent in the population made me happy.

He was really quite fat and had no protrusions. He’s also in the tank with 2 juvenile seahorses. I was very tired last night and after turning the filter off to feed both animals, I accidentally left it off overnight. I got up, turned it back on and the mandarin was on the sandbed flipping over as if he had a horrific swim bladder issue. I watched him die in the corner of the tank.

I did all 3 tests (nitrate/nitrite/ammonia). Results were 10/0/0 respectively. I’m 95% sure it was the filter but the seahorses are perfectly fine. I should also mention that I lost a Midas Blenny around 3-4 months ago with what I think was velvet as he was swimming into the power head. At the beginning I treated with Prazi when he had fluke like symptoms. Once the 2 prazi treatments was over that is when the Midas Blenny swam into the power head and died shortly after. I kept the tank unoccupied of fish for 6 weeks. The mandarin showed no signs of disease whatsoever and I should finally note that I did not know if the Midas Blenny had velvet for sure. I received many many different answers from different specialists so I’m still not sure to this day.

 

[Jay Hemdal]

Welcome to Reef2Reef!

Based on the pump being off, my first thought was low oxygen and/or high carbon dioxide. Do you have any secondary aeration in the tank like an air stone? I also wonder about the Midas - prazi treatments also pull oxygen out of the water, so if your tank is lacking aeration, prazi would have the same affect as leaving the filter off.
I can’t explain however why the seahorses are fine, perhaps they don’t have the same oxygen demand as mandarins?
Jay

 

[KeepSwimming12]

Welcome to Reef2Reef!

Based on the pump being off, my first thought was low oxygen and/or high carbon dioxide. Do you have any secondary aeration in the tank like an air stone? I also wonder about the Midas - prazi treatments also pull oxygen out of the water, so if your tank is lacking aeration, prazi would have the same affect as leaving the filter off.
I can’t explain however why the seahorses are fine, perhaps they don’t have the same oxygen demand as mandarins?
Jay

Thanks for your reply! I don’t have any secondary aeration. I think the Prazi might be out of the tank as I’ve done quite a few water changes since then and also use carbon but I’ve definitely heard that it reduces oxygen in the water. I think you might have a point in regard to the mandarin having different oxygen requirements. I also have a Flame Hawkfish and Midas Blenny in different tanks and they definitely require more oxygen so maybe the mandarin couldn’t tolerate that low of a level. I only hope it wasn’t disease but it would be a big coincidence.