I bought some new zebra danios for my 20 gallon tank today, and one of them died within an hour and 30 minutes of being introduced to their new tank. (I allowed them to acclimatize in the bag as usual.) I removed the dead fish and immediately noticed it had some tiny red spots on its body. Upon closer inspection, I noticed these spots covered the majority of its body and were most visible on its belly. The fish had no other symptoms I could see other than being slightly pale. I immediately removed all of the other zebra danios and placed them in a 10 gallon hospital tank. I am currently raising the temperature in that tank to 80 degrees F, removed the carbon filter, and I gave them a dose of Metroplex. (Metroplex is a treatment for protozoan and bacterial diseases, and the active ingredient is metronidazole.) I also gave the original 20 gallon tank a dosage of Metroplex and removed the carbon filter as well.

I hope to God this is not hemorrhagic septicemia. There were not red streaks in the fins, and no fin or mouth rot was visible.

Please help me identify this disease! I currently own a 20 gallon tropical community tank with a school of black neon tetras and albino corydoras. The water is typically 74 degrees F and has no salt treatment. The nitrate/nitrite levels are minimal, and the water is slightly hard with an ideal alkalinity.