When you are treating your fish in the 2gallon tanks using medication it is a good idea to use an air stone. That way the medication is moving around the tank and not laying at the bottom. Also use a mini-heater if you can it helps with healing. As far as the extra carbon hurting the fish...I haven't had any problems...you can add half the required dosage if you would feel more comfortable and see if it's enough. It generally takes about one to three days for my tanks to clear up completely after adding additional carbon. You're also supposed to change it every six weeks. Basically what the carbon is doing is absorbing pollutants. I found this article that explains it a little better. http://www.ratemyfishtank.com/articles/106
As for the carbon being unsightly, no, because you need to put it in a pouch/ bag (I just use old stocking/ pantyhose and cut out a square than put the activated carbon in it, tie it in a knot, rinse it well and than place it within the back of the filter with the other carbon.) It shouldn't be seen at all.
About the airstone helping to reduce cloudiness I didn't notice that help me out at all. If anything it just stirred more stuff around, lol but I think that varies from tank to tank. Betta's don't need an airstone anyway and prefer stagnant water, sometimes the filter is even too much. And good idea for not listening to them because most of the people hired are young with no background. Sometimes it's just a better idea to research yourself.