I asked my breeder friend about this disease, he knows better than me what we have locally and what we don't. This is what he suggested, I'm not starting to treat before you guys okay it anyway.
He told me to use a 2 liter PET bottle to keep the fish while treating. (seems nice because changing 100% of 20 liters daily while I don't have a siphon yet seems a lot of work)
To add to the water a dash of regular salt (aquarium salt can only be purchased at large 1kg quantities).
And to add also two other medicines that they sell at my local fish store: one is called "aqualife" and the other is called "anti ictio". I have no idea what the names of those would be in English, I tried googling it with no success.
The Aqualife I already have and I used it to treat this same fish's fin rot. The webpage of the manufacturer (http://www.labcon.com.br/peixesaquar...s/aqualife.htm
) mentions it is used to treat "velvet" also.
This other one I cannot find info on, but google says "Ictio" is "Ichthyophthirius multifilis
My friend advised to keep the fish from any light on the first three days, and I should re-treat for another 3 days if the first 3 days don't work.
I have no idea what "dechlorinated" is? Is it just water?