Hmm, this is a predicament

Whirling Disease or Fin Rot

Whirling disease...,
The fish loses equilibrium and whirls about dizzily. It cannot maintain itself in a normal swimming position. It is caused by a protozoan (Lentospora cerebralis). By the time the fish begins to whirl, the disease has already penetrated the cartilages of the skull and destroyed the part of the brain which cotrols the balancing power of the fish. Its recommended that you sterilize all equipment but i wouldnt go that far unless you notice it effecting more of your fish. Another possiblilty is Fin Rot. The edges of the fins become cloudy and white, and begin to fray. The fins then become reddish and inflamed and the fish will finally succumb if untreated. Fin rot usually occurs as a result of rough handling or because of to high pH that burns the fins and causes phsyical damage. Fin rot is best prevented by maintaining good water quality. Water polluted with fish wastes incourages bacteria growth and if enough infectious bacteria are in the water they will find an openin somewhere in the fish's defenses.