Enough is enough! After encountering recent failures to eradicate uronema via metronidazole, acriflavine and FW dips; I highly recommend using formalin to pretreat any chromis and other Uronema prone fish. Anthias are also very susceptible, but I sometimes see Uronema on damsels, clownfish, butterflies and angels.
Any fish you suspect is carrying Uronema should get a 45-60 minute formalin bath before entering your DT or QT. Do the following:
- Buy 37% Formaldehyde which also contains 10-15% methanol as a stabilizer. Amazon sells it here & here.
- Buy waterproof gloves and a face mask. To prevent your skin from coming into contact with it and to protect your lungs from the fumes.
- Use a bucket or small aquarium to perform the 60 minute formalin bath. Temperature control the water by using a heater. It is very important to heavily aerate the bath for at least 30 minutes before and also during treatment to compensate for oxygen depletion. The fish should be placed in a premixed bath solution. DO NOT add more formalin after the fish is already in the bath.
- Dosage for the bath is 0.6 ml per gallon, or 12 drops per gallon.
DO NOT use formalin (or H2O2 for that matter) on fish with open sores/wounds. It will burn them. This treatment is designed to treat fish who are carriers (light infestation) of Uronema. If you see active red sores on a chromis, humanely euthanize the animal: https://www.reef2reef.com/threads/how-to-euthanize-a-fish.266222/
If you have an aversion to using formalin, I would just avoid chromis altogether. It's not worth getting a free living parasite in your aquarium that going fallow will not eradicate. Uronema in high concentrations can affect ALL FISH; attacking the gills, viscera and body muscle.
There is anecdotal evidence (but never scientifically proven) that some fish exposed to formalin don’t live past 18-24 months. In some areas, the purchase of formalin is prohibited.
If you need confirmation of Uronema, take a skin scrape of the affected area and examine under a microscope. Compare to what you see below: