Guppy Losing Its Tail

[DrKebab]

It's been about a month and a few weeks since my tank has cycled and I put a few fishes in a few days ago, including a few guppies. There's one particular guppy that's really restless. Ever since I've gotten it, its been on the top swimming against the current that my bubbler makes. It's been doing that for a few days non-stop now and I was worried because I put it in a divider and I realized that its whole tale was gone. I'm really worried that whatever caused it could spread to the other guppies. They've been doing great, hiding and playing and resting. But this guppy I'm really worried about. What can I do to help the guppy losing its tail? Ammonium = 0, Nitrate = 0, Nitrite = .25, 30gal tank, pH = 7.2

 

[WILDER]

Your tank has a nitrite reading so the tank hasn't cycled.
Immediate water change and increase aeration in the tank.
How many fish and which type do you have in the 30 gallon.

Once a guppys losses half of its tails they tend not to make it.
How much of the tail has gone.
Bad water quality causes finrot.
Any red streaking in the fins, or red edging to the tail