One heck of a disease?

Question
Alright well first off here are my statistics
-33 gallon freshwater aqaurium that has been set up for about 4 months.
- 2 bullhead catfish, 1 leapord catfish, 2 plecos, 1 perch and a small mouthed bass
-some water lettuce on top of aquarium
- all neccessary equipment and heating
-feed shrimp every day, everyone loves it.
-I do a regular water change about once every two weeks or so.
-all chemical levels are fine

OKAY so this problem has been going on for awhile and it has been slowly killing off my bass.  I'm down to my last one and I plan save him!  Now the symptoms have only seemed to affect him and everyone else is fine until just yesterday I noticed my perch has a white substance growing on his fin.  Some of the things wrong with my bass are: fins rotting, very pale, pink gills, either floating at top or bottom of tank, loss of appetite, almost confused swimming, not active and whats most concerning is very rapid breathing.  Now I know that local fish are probably not up your alley but the diseases are still the same.  The only symptoms my other fish have is the rapid breathing but that seems to be improving in my catfish.  Now I have been trying to narrow it down and I have ruled out ich for sure.  I have also been treating it with coppersafe for about 2 weeks now with temperature raised and added aquairum salt with little improvements.  My main concern is to help their gills regenerate.  Anyways I have finally given up and have turned to you for help.  I'm hoping you can narrow down my search for the right disease/parasite/fungus.  Also I'd like to mention that there is no salt like substances on their skin.

Thanks a bunch!
Mike

Answer
Hi Mike;

The system could be too low in oxygen. Perhaps the bass tolerate it less than the others, maybe having higher oxygen requirements. I just don't know enough about them to say. It's also possible they all had a gill disease and the damage was just too severe in those particular fish for them to survive much longer. Gill damage, just like lung damage in animals and people, can be progressive or simply cause a chronic oxygen absorption problem that slowly causes  brain damage and eventually death. You could add an extra filter and/or an airstone to agitate the water more and help with the oxygen levels.

The tank is overcrowded actually too so that alone can be the cause of a low-oxygen condition. Most of your fish are messy guys that will get very big so their waste could easily be too much for a 33 gallon tank already even if they are still small. It's only going to get worse as they grow. Make more frequent water changes and vacuum the gravel too. All freshwater tanks need a 25% water change and gravel vacuuming once a week, every week. It can be done more often if there is a lot of waste.

Hopefully this has helped you somewhat. Let me know if there is anything else I can do to help...

At Your Service;
Chris Robbins