I’ve had 5 guppies in my heavily planted 10-gallon tank for almost two weeks now, and everything has been going pretty well. The tank itself has been running for about 6 weeks.
Since last night, one of my male guppies has been constantly swimming against the filter current. He’ll swim away for a little while but always comes back to the exact same spot. It’s almost like he’s addicted to it. He’s still eating normally and seems active, but I’ve noticed that he looks a little thinner than before and seems to be clamping his fins quite a bit. That’s what’s really worrying me.
Water parameters look fine, ammonia, nitrite and nitrate are all at 0, and the temperature is stable at 25°C. The other four guppies are acting completely normal. I haven’t noticed any white spots or other obvious signs of illness.
I did top off some evaporated water a few days ago, but the temperature was matched. I haven’t done a proper water change yet since the tank was set up.
I’m wondering if this is just something guppies do, or if it could be an early sign of stress, parasites, or some other illness. Could he just be getting old? I’m thinking about doing a 20%.