I will make some 10% water changes every day then.
If it’s not too inconvenient, I’d recommend daily 25% water changes
I’d not rush to sell off your serpae tetras (assuming you like them), while they can be nippy, kept in sufficient numbers and suitable tank size, they can be good community fish
(I’m also somewhat concerned that the dwarf gouramis you purchased may have health complications - dwarf gourami iridovirus is very common (but is less likely to affect other fish in the aquarium as long as water quality etc is good) and they are one of the species where Fish mycobacteriosis strains are prevalent in aquafarm stock (again good water quality is the best protection for other fish in the tank, also some fish species are just less susceptible.
If you observe any ulcers, remove fish from a community tank re increasing severity of disease)
An example of a DG I would euthanize
- although fish is reportedly eating well, he is quite emaciated through head and body, is clamped, has visible red ulcer, also body appears “dusted”
If you did not want to euthanize this fish (as shown in the linked photo), a bare isolation tank with some artificial wood (so fish feels more secure), and medicated food might improve his health, I’d begin with levamisol~food, daily 50-75% water changes including wiping down glass surfaces ... then depending on fish response, add some antibiotics to his regime - perhaps a kanamycin bath (still maintaining daily water changes and refreshing bath medication) while still feeding the levamisol~food (which is well tolerated by most fish and remains relatively palatable)
Again depending on fish behaviour, an external parasite treatment might precede antibiotic treatment (observed clamping may be symptomatic of external parasites or internal bacterial infection ... both are likely present to some degree)
If after a couple weeks treatment, fish appeared no better, I’d euthanize; if fish improved, I’d slowly withdraw medications while maintaining fish in isolation ... as both “most likely” diagnoses are terminal, I would keep this fish in isolation but eventually move him to an aquascaped tank, maintaining optimum water quality
At intervals, a return to medicated food is usually required, eventually fish will stop eating (I euthanize at this stage)
Note the medicated food and bath is only supportive care that may reduce secondary infections, it does not “treat” iridovirus or mycobacterium sp.
A somewhat depressing read, (written as a summary article so fairly user friendly
) which includes disinfection protocols
Mycobacterial Infections of Fish
Ruth Francis-Floyd
From
Aquarium Glaser Serpae Tetra
From a scientific point of view the Serpae tetra is subject of a controversial debate that lasts already for more than 50 years – and still no satisfying solution has been published yet. How many species cover behind the common name of „Serpae tetra“? And what is the correct scientific name for them? So hobbyists interested in tetras will for sure be happy that we were able to import now some wild collected specimens. They originate from the surroundings of the city of Cuiabá in the state of Mato Grosso. Currently these animals are about 3 cm long and thus not fully grown and not full in color yet, but very healthy and lively.
The import happend in July 2017. We kept some specimens in our fishhouse to see what would become of them. They go for sale now, too. The fish became very nice, graceful Serpa tetras. The most remarkable thing is that they are very peaceful against each other. Of course the males display against each other (as it is usual in the tetra family), but they don´t even hurt the finneage of the competitor, as it sadly often happens in aquarium strains.