I treated the tank with Furan-2 yesterday afternoon and I woke up this morning to find out several fish are dead and many other infected by bacteria.

So the antibiotic medication Furan-2 doesn't work. All my fish are subjected to death sentence.


What else can I do instead of watch them die one by one?

It's a 20G planted tank and bacteria infection almost wiped out the whole tank last week with two fish survived.

I add couple new fish in on Friday and thinking the problem is gone since I had left salt in the tank for couple of days and those two survived fish seem healthy. I also soaked all the plants in tap water for couple of days as well.

Now all the new fish are still infected by bacteria and many of them are dead.

Temp: 80F. pH: 6.8 and no ammonia or nitrite. I did a 75% w/c change before the Furan-2 treatment yesterday.

I'm speechless.

32Bit ~I'm so sorry I'm going to move this to the diagnosis forum and answer you over there. I assume you are talking about goldfish? (this is posted in the tropical fish section at the mo).

My tropical tank, cardinal tetra and red rummy nose.

Thank God, my gold fish are fat and healthy.

Goldfish or tropical ~ Furan-2 is a difficult medication to get precisely right when dosing. One of the problems with it is that it is a combination medication combining 2 antibiotics with a disinfectant fungicide (meth blue). The two antibiotics in Furan 2 moreover are listed by the FDA as unapproved for treating food fish, meaning they are known to be carcinogens and among the most potent/longest withdrawal period (stay in the fish the longest time + are hardest for the fish to eliminate) antibiotics for fish.

By combining 2 very powerful and harsh antibiotics with meth blue you have one of the most deadly and powerful weapons against all protozoa and many bacteria. However because of the combination factor you also have a drug that has a very low toxic threshold for the fish themselves. This is going to be even more relevant with small fish and worst with tiny tropicals.

Because of Furan's ichthyotoxicity it should be used with great caution.

* Not to be used for systemic bacterial disease (internal) but can be effective for surface bacterial disease.
*Fish size should be considered and dosage adjusted accordingly.
*High water temperatures will also increase toxicity (yours at 80 is high) as will acidic pH (yours is 6.8).
*The margin between therapeutic levels for fish and safety is very slim with all combination type drugs and need not only adjusting but also monitoring- in other words you need to watch the fish for at least 2 hours after administering.
*Fish will show signs of intolerance (bottom sitting or off kilter swimming/gasping for more than 20 mins after adding meds warrants a complete water change and a re-think of medication).
*All meds must be used with extra dissolved oxygen- especially at high temps - the fish die of hypoxia (suffocation from lack of DO) faster than the bacteria do.

So to sum up, I don't know that this set of circumstances can be ascribed to antibiotic resistance but rather to the very tricky negotiative juggling that is necessary when using Furan 2.

Thanks for the info. I guess there is nothing I can do at this point.

I never had luck treating bacteria infection, it wouldn't be a exception this time either.