It could be fungus or it could bacterial infection. Fortunately for me, unfortunately for you, I've never had to deal with that particular issue so I can't really be of much assistance.
Ultimately, I think it all comes down to stress and water quality though. If the water is kept clean, many times the fish can fight off these types of things pretty well on their own. If not, then it can get much worse. I can't recommend meds personally, but I've heard Rid-Ich does the job very well. In the meantime, I would keep up with the water changes to remove the cysts of the ich parasite before they even get a chance to get to the free swimming stage (lots of gravel vaccing!). Large water changes will also help to improve the overall water quality, while removing the free swimmers as well and help to relieve some of their stress. The down side is that you will also be removing their meds to kill the free swimming ich. So, you need to redose as directed.
Have you added any salt to the tank? I'm not sure how the pleco will do with the salt, but the others should be fine with it. (You don't have corys do you?) Some folks treat ich with only heat, salt, and water changes. Ich dies at prolonged exposure to 86 degrees, I believe. If you can't go that high for fear of killing your fish as well, then just bump it up as high as you are comfortable with. The heat may be a little stressful, but it will increase the life cycle of the ich, so that it leaves the fish and heads towards that vulnerable stage for the meds, or to where you can vac it up. The salt can help the fish as a tonic and the ich don't like it.
Ultimately, I think the only thing you can do to combat this is water changes and LOTS of them 50% per day every day until the ich is gone. Keep vaccing up the cysts on the gravel and removing the free swimmers from the water. This will reduce the number able to attack your fish. If the air stone is bothering them, try dropping the water level a bit so that water from the filter output splashes into the tank. It might be a little noisier, but the increased drop will better aerate the water without all the bubbles that seem to be disturbing your fish. The last thing you want to do right now is offer them any more stress.