White minnow not swimming
Yesterday I introduced 5 white could minnows to my 20 gl cycled planted tank. Nothing else in there except for 2 assassin snails. I acclimated them and as soon as they were released they were active, playing and exploring all over the tank. This morning one of them is acting weird. Not swimming around, just hovering mostly near the top but not gasping for air, just being still with the occasional tail and fins twitch. He seems to let himself be moved around by the water current. He's not bloated, not pooping as far I I'm observing, no strange marks on the body and posture not quite horizontal, head a bit upward, tail downward. He's not hiding either, even though there are plenty of spots and plants. Right now he's hovering mid tank in the middle.
The other 4 are horseplaying around.
Tested the water today, everything seems on order. Temperature is around 75 degrees. Ph 7.6
What could have happened to him since last night when he was just as active as the others ? Is presenting sings of what ?
Never had cloud minnows before.