Hey guys, So I am at a loss on this one. My fish (black neon tetra) has a red fin, also maybe signs of fin rot? I don't know. I have just done a 3 day meds cycle with a 25% water change today. Info: Ammonia 0ppm, Nitrite 0ppm, nitrate 20 ppm. Tank size 40 liters, filtration is a dual sponge filter rated at being able to filter 140 l/h. Temp is 25.3 degrees. Heavily Planted and is stocked with the following 10 blue carbon rili shrimp 2 black neon tetra 2 dwarf puffer All other fish seem healthy, only that one has any signs of being unwell. I have included a picture to help.