Pale gills can be bacterial gillrot.
Bacterial Gill Disease
Bacterial Gill Disease, also referred to as "BGD" is when the gills of the fish are eaten away by bacterial infection. To check for this disease, carefully pull back the gill plate enough to examine the gill tissue. It should be red and smooth with even edges. Signs of the disease include pale gills and frayed edges. The tissue itself may appear "moth eaten". Although bad bacteria cause infections and contribute to the death of the fish the bacteria themselves do not actually initiate the disease. It's other things. BGD can develop through overcrowding, parasitic infestation (most likely Flukes) and poor water quality. It is spread from one fish to another and can come in with new arrivals. The best way to treat BGD is to get rid of whatever is causing it then treat the symptoms. Find more information on bacterial diseases in our article, "Battle of the Bacteria".
Since BGD is initiated by poor water quality, parasites and/or overcrowded conditions you must first correct the problem that's causing it. #1 - Test the water for pH, Ammonia and Nitrites. A master test kit is available that will cover all these very necessary tests. If you find any readings of ammonia or nitrites, fix the problem! If you pH is not between 7.0 and 8.0 and/or is not stable, correct it and stabilize it using pH Stabilizer. #2 - If the water tests are fine then look for signs of parasites. If parasites are suspected then it's most likely Flukes and, to be on the safe side, I would treat the pond for Flukes using Anti-Fluke or Fluke Tabs and Perform a Salt Treatment at the same time. #3 - Treat the disease itself with Chloramine T. NEVER USE MORE THAN ONE KIND OF TREATMENT AT THE SAME TIME - THIS WILL RESULT IN FISH DEATH. The only exception would be the salt.
/www.thetropicaltank.co.uk/hdgilld.htm
