I recently got a beautiful veil tail Betta who I unfortunately noticed has fin rot. We spoke to the aquatics place I got him from and got our water tested and everything was perfect, leading us to believe he had it when we bought him. His fin rot looked quite severe to me as I woke up on morning and he had lost quite a bit of his tail.

The shop recommended to me Myxazin in which I gave him the correct dosage for 5 days. He appeared to be improving. I was a bit apprehensive to take the carbon filter out as really I didn't want to ruin the water quality of my tank, but did as I was aware the Myxazin wouldn't work otherwise. The plants in my tank and a bit of the side of my tank has brown marks on which I'm presuming is from the Myxazin but it seems easy to remove. After the five days I waited a few more to put the carbon filter back in and do a water change.

All was going well until I woke up yesterday morning to my Betta's tail being gone again, however this time it was much worse, and even a bit of his top fin was on the bottom of the tank. I panicked and have started him on the Myxazin again, and though there are signs of improvement, I'm worried that if I stop the treatment and do a water change after 5 days and put the filter cartridges back in he will just deteriorate again.

  • Welcome to Pets SE. Have you been back to the aquatics store since you picked up the Myxazin? Can you add a photo of the Betta's current condition?
    – elbrant
    Jan 24, 2019 at 2:08

1 Answer 1


The ideal way to treat sick fish is to use a separate tank for the treatment. You take the water from your original tank and fill this in the tank where you want to treat your fish and add the medication.

The reason for doing this is to be sure the bacteria in your tank (where you normally keep the fish) will continue the nitrogen cycle and keep the water clean and free of toxins.

This will mean that when the treatment of your fish is over and you put the fish back into the aquarium it will have a better chance of surviving.

The things you need for a quarantine/treatment tank is an air pump and an air stone plus an aquarium heater. You will need to cut back on the feeding of your fish during the time you treat it.

I do know I have not answered the main part of your question and that you are treating the whole tank. The problem is by treating the whole tank you have killed the bacteria needed to convert waste into nutrients and this is a big problem so even if your fish is healed from the illness it might die from the toxins produced in the tank as a result of the lack of the bacteria needed to keep the nitrogen cycle going.

The use of a carbon filter in a tank is only useful for removing medication or chemicals. It does not remove ammonia-nitrite or nitrate from the water (carbon filters do waste space in your filter that had been better used to grow useful bacteria in your filter) so unless you are removing medication from the water you do not need it. https://www.thesprucepets.com/activated-carbon-in-the-aquarium-1380929

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