Can't figure out what the problem is...
I have a 20 g fully cycled tank with a penguin 150 bio wheel and an air stone. Water tests are reading well, Ph 7.8, Amonia, Nitrates and Nitrites 0.
I have one felmale platty that I've had since September who a few days ago started just hanging out around the surface. Pretty much all of the time. Just hanging out. She will still eat, but mostly stays at the surface except for the occasional venture around the tank.
I did a partial water change even though levels looked good. No change in her behavour, and tests are still reading the same.
Yesterday, one of my male plattys joined her and has been by her side ever since. She does not look pregnant, if anything, rather thin, as does her male friend.
Today, her fins seemed to be "clamped", but the male's fins still seem to be ok. She is still eating, with the occasion tour around the tank, but the fins and tail don't look good. No white spots or any other obvious disease that I can see.
Aside from these two, my other aquatic creatures seem to be doing well. I have two other female plattys, 4 neon tetra and 6 ghost shrimp.
Any suggestions on what the problem might be? I really don't want to be killing fish if I can avoid it.