First, please understand that there is no such disease as "bloat." Bloat is a symptom, not a disease, and treating for bloat is like treating a person for "runny nose." It can be caused by many different things, and the treatment will vary significantly.
Bloat is caused by a build up of either gas, or more commonly, fluids inside of the fish's body. Rarely, it is caused by a growth in the fish, which can be egg mass, parasites, cancer, and even pregnancy (I've had customers try to treat pregnant livebearers for bloat!). Gas build ups will cause bloating, but this usually comes with buoyancy problems, and is typically described as "swim bladder disease," which can be bloating or a bunch of other things. Fluids will build up in the tissues of your fish for a lot of reasons. In Malawi mbuna, and particularly in their Tanganyikan cousins, this can be triggered by poor diet, but the main reason is probably the same: failure of the kidneys. This is the number one cause of bloat, and I would say represents 95% of actual cases.
Now, what's causing the kidneys to fail? Processing too much protein does it. Certain bacterial infections. Stress. Genetics. Bad mojo.
Generally, its not contagious. If more than one fish is displaying symptoms, you should check your water quality, nutrition, and other factors first. Even if it is a parasitic infection, they're seldom virulent. They have to reach an incredible critical mass before they really harm the fish, and its unlikely that numerous fish will be displaying at once -
unless something else is wrong. Remember, its a poor parasite that kills its host. Bloated fish are stressed fish. Fix the stressor.
Stressed fish are more susceptible to all sorts of diseases, including ich. Ich is very easily fought off by healthy fish's immune systems: unstressed fish rarely, if ever, get ich. If the fish are coming down with ich, something is stressing them out. A new fish, bad water conditions, etc., including being exposed to a fish that has an ich infection (e.g., if you buy a fish at petsmart and toss it in a tank of healthy fish, that guys gonna get ich, and then everyone else is.). So, somewhere in your tank you have a problem, and need to figure out what it is.
I wouldn't worry about "treating the whole tank for bloat." I would attack the ich, vigorously, and then try to fix what your tank problem is. Raising the temperature over 24-48 hours to 88°F, keeping it there for 5 days, and then decreasing it to normal over another 3-4 days will eliminate ich with no other medication. You
must increase aeration in a heavily stocked tank. You cannot do this on really badly infected fish, as they generally will not survive -- the crux of it is that they'll generally not survive anything you do to them. :-/
Goodluck!
