Dwarf Spotted Rasbora illness

[idleivey]

I have a 20 gallon planted tank that has been running for a couple months now and I recently been having issues with my Dwarf Rasboras. They had been in a 15 gallon for a year or so prior with no issues. I've lost two recently both to the same illness. They start to turn black and waste away despite healthy eating. I have been dosing my tank with Sulfathiazole per advice from my LFS but another rasbora has started to show signs of illness.

I plan to isolate the rasboras in my hospital tank but not sure how to treat. I haven't seen any symptoms in tank mates. Water parameters are good, 0 nitrite, 0 ammonia. I have a fluval 305 filter and I am running mechanical filtration media. Any help would be appreciated.

 

[Rbishop]

What and how many on the tankmates? Liquid test kit? What illness are you assuming?

 

[idleivey]

Tank mates are lampeye killies, tetra cardinals, a betta, dwarf pleco and Australian goby. Yes I'm using liquid test kits. On the affected rasbora I have been noticing what look like sores? I was thinking maybe TB but at this point I have no idea.