Having had relatively good luck raising and spawning fish, seeing anything die is distressing. Yes, I’d had a fish get beaten up, or a one mysteriously die (presumed old age), or that one species I could never seem to keep (but no clear plagues or diseases). I’d even bought fish with ich and successfully treated them. Had a bout with roundworms in which two fish died but the rest of the tank survived with treatment. But I wasn’t prepared for the black cloud that blew in last fall.
I had a tank of Pelvicachromis subocellatus fry that I had raised up to spawning age. I was admiring their color and how it was actually better than their parent and was musing that perhaps I should keep some of the kids to spawn. Mixed in with them were a handful of mostly single full-grown dwarf cichlids, including Apistogramma nijsseni, A. norberti, A. sp. "breitbinden", A. steindachneri, and P. taeniatus.
They were all in a 20-gallon tank with numerous floating and bogwood-anchored plants: Java fern, Java moss, frogbit, etc.
I used to do water changes every 1-2 weeks, but with my hectic work schedule it was lagging to every 3-4 weeks. Everyone looked well, and nitrates were under control (< 10 ppm).
One day the taeniatus died. I wasn’t worried; she was old.
Then about a week later, I noticed one of the subocellatus breathing heavily and losing color. The next day it was dead. Then another. A fish was dying about every other day. I started to rack my brain. I had done a 50-60% water change.perhaps that was too much. Nitrates were OK, but a pH test read below 5. Perhaps the water was too soft.
Two weeks prior to the deaths, I had fed the last of an old package of frozen bloodworms, but otherwise all they got was baby and adult brine and flake food. No new fish had been added.
The other tankmates looked great until they too gradually developed the fatal rapid breathing and color loss. We added some carbonates (MgCO3) to harden the water and did frequent water changes. We poured through fish health books with no clear answers, and finally called Steve Ward, our local disease expert. He generously donated his time to dissect one of the sick patients and found all evidence pointed to Gram Negative Rod Sepsis-Bacterial Infection.
Relieved to have a possible diagnosis, we treated the fish with Antibiotics. We still ended up losing several other fish and are now down the four bachelor Apistogramma specimens. At this time, there’ve been no further deaths for 2 weeks.
Hopefully this tale is over. In retrospect, the package of bloodworms fed was one we had meant to toss-it had been partially thawed and refrozen. Most likely it had a high bacterial load and was the source of the problems. No other tanks have shown signs of the infection.