What is the temperature of your water?
is the fish biting it's own tail? seems bad for one night.
Tail Biting
Syndrome : There are two suspected causes namely,Bacteria Infection on Tail due to poor water quality or bacterias introduce from feeders (esp frogs) or tank mates.The fish tries to reduce itchness by biting its own tail. The fish mistaken the tail as another fish and starts to attack the intruder which happens tp be its own tail. The condition can be improved by switching off the tank light. Symptoms : The fish bites its own tail. The end result would torn and uneven tail fin. Remedy : Immediately change water, provide more aeration, add more air stones to increase the level of dissolved oxygen in the water.Change the filter.Raise water temperature to 34°C gradually (1 degree over 2 hour). Add 1% coarse salt to the water. Add commerically available fin rot solutions. .Change water everyday (20-30%) for 3-6 days to maintain good water quality. If condition doesn't improve, introduce other attractions to the tank, eg, place a mirror near the tank to distract its attention or introduce another tank mate (parrot fish etc).If tail biting never ceases, the last option will be to perform a tail cutting operation on its tail. However, in many cases, the tail will not regain its previous glory after the operation. It is adviseable to get a professional to perform this operation and many local fish shops do provide this service for S$50.
Tail Cutting Procedure. Transfer the fish into a "holding tank; with very low water level(about 3-6 inches above the fish) , add naesthesia
into the tank drop by drop.Watch the fish for few minutes before adding another drop, never overdose especially when administering anaesthesia!Once the fish loses consciousness, remove the fish and place it on the clean damp cloth.Use the scissors(make sure sterilized) to carefully trim of the affected tail fin by following the fan shape contour of the fin. Place the fish back into the tank and increase the amount of dissolved oxygen in the tank, if necessary direct the airflow of the airstone towards the gills of the fish to help accelerate consciousness.After regaining its consciousness, let the fish rest and off all lights so as to let the fish recuperate under dim conditions.Feeding is not required if the fish shows no signs of interest in food.Change water everyday (20-30%)for 3-6 days to maintain good water quality.Salt may be added to reduce parasite attacks and help to increase recovery rate.
Fin Rot
Cause : Bacteria Infection on fins due to poor water quality or bacterias introduced from feeders or tank mates. Symptoms : The fin edges become pale and start to rot. Remedy :Immediately change water, provide more aeration, add more air stones to increase the level of dissolved oxygen in the water.Change the filter.Raise water temperature to 34°C gradually (1 degree over 2 hour). Add 1% coarse salt to the water. Add commerically available fin rot solutions. .Change water everyday (20-30%) for 3-6 days to maintain good water quality.
This information has been cut and pasted from "MFK arowana disease and cure" thread.
Hope it helps.