Resistent Fin rot / columnaris

I have a discus stock with 30 adult and medium discus fish. They got finrot for a week ago, when i noticed this i turned temp to 28 C. And started treatment with Api triple sulfa - and Kanamycin ( kanaplex) after one week of treatment with these medicines, theres is no improvement. The finrot seems to be a hard strain... after reading your advice here in this thread i started to move them to the quarantaine tank. They got 8 table spoon salt ( tripond salt for koi fish) to my QT tank 20 galons.
After one day of treatment The slim coat seems a little darker( burned like) ....should i still continue for a full week treatment or should i stop and try other anti bakterial medicine?
I have had this finrot disease last year,,,and i was not able to cure the fish. ( it was another stock, not the same as now)
I used at that time Furan 2 , Antimicina, Oxitetraciclina , triple sulfa, Acriflavine, Mardel Maracyn Plus. All of these against gram negative bacteria,,without success in fighting this aggressiv disease.
please tell me what should i do now?
Thank you in advance.

Not sure about the type of salt you used but sea salt is ok.

I think initially your temp must be way too low and it allows all sorts of problems to set themselves up. My system has set at a minimum of 30 degrees and if I did ever have a problem I would QT at up to 33 degrees.
You don't mention the volume of your system but with the amount of fish you have it must be quite substantial.... ? What is your water change regime? So much we don't know to give you more advice.

thank you for your comments... i have my QT tank at 29 C now ...i read high temps encourage the bacteria to grow faster..i have treated my tank with koi salt for pond;
https://www.amazon.de/TRIPOND-Teichs.../dp/B009AVRUJO is this salt ok?
i change the water once a day during this issue and add the salt and acriflavine.
all my fish has strong dark slime now. .is it normal??
all the fish gathers in the corner and are dark��

the tank is 100 liters and 15 fish now..5 adults the rest small...i change water and treat it every day.

You are way over stocked for the size of your tank ,the rule of thumb is 40 liter for an adult fish and i think this is the root of your problem , you might solve the fin rut problem temporarily with various antibiotic but it will comeback again , i have no easy solution in mind ,you simply have too many fish for the size of your tank. sorry .

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Originally Posted by sayid

You are way over stocked for the size of your tank ,the rule of thumb is 40 liter for an adult fish and i think this is the root of your problem , you might solve the fin rut problem temporarily with various antibiotic but it will comeback again , i have no easy solution in mind ,you simply have too many fish for the size of your tank. sorry .

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Yes I agree with you Sayid