Hi Minkypoo,
Sorry bout your fish. What happened or changed recently to stress your fish? Have you recently introduced a new fish to the tank? Just trying to figure out the cause. Are you doing partial water changes on a regular basis? Sounds like you have some really big and dirty fish in an overcrowded aquarium. Here are some things you could try:
1. Do a thorough gravel vacuuming while changing 25% of the water in the tank.
2. Slowly increase the water temperature to 85 deg F or 29.5 deg C. Increase the temp SLOWLY, like one degree every four hours.
3. Increase the aeration in the aquarium. The higher temps will cause your dissolved oxygen levels to drop so you'll need increased surface agitation. Airstones will do the trick or if you can increase the flow rate of your filter that will also help.
4. Get rid-ich and follow the directions exactly. You will probably need to treat your aquarium for a week or longer.
5. Do those 25% water changes with gravel vacuuming every couple of days.
6. Monitor your water parameters for ammonia, nitrite and nitrate because the use of medicines may cause your aquarium to re-cycle.
7. If you aquarium does re-cycle you'll need to perform frequent water changes until the aquarium finishes cycling.
Also - check out the following links for more information:
http://www.fishlore.com/Articles/SickFish.htm
http://www.fishlore.com/Articles/CuringIch.htm
http://www.fishlore.com/NitrogenCycle.htm
http://www.fishlore.com/QuarantineTankSetup.htm
Hope this helps. Let us know how it goes.
Mike