z

7. Fish look slimy, covered with white slime.

 Slimey white areas are never a good sign.  In fresh water aquariums it could be a secondary response to a parasite or injury.  It could be a bacterial infection.  It could be the fish's natural response to poor water quality.  None of these can be ruled out until you know that your water quality is good.  Salting the aquarium will rule out fungus and performing water changes will improve the water.

In salt water (as shown in the picture) this is almost always caused by Brooklynella or Amyloodinium.  These two parasites are somewhat common in the marine hobby and can usually be treated with a copper based treatment or formalin.  In reef aquariums, removing the fish and treating in a quarantine tank is the only option.  Bacterial infections can not be ruled out but treating with copper is always your best bet.

A clean environment is always helpful allowing your fish's natural immune system to fight off any infections.  Maintain your tanks!