chronic deaths

Question
I have been experiencing a slow chronic death of the inhabitants in my 55 gal aquarium for the past 3 months.  The tank has been up and running for 9 months and although that is a short time I have kept serveral tanks over the past 5 years (135gal, 55gal, 10gal - all freshwater tropical community) with no problems before.  The fish get white fuzzy patches around the mouth and sometimes sores on the body that are red.  I do a 25% water change weekly and a gravel vac every 2-4 weeks.  The ammonia level is good, nitrate -0, nitrite - 0, hardness - 250ppm, alkalinity - 300ppm, ph 8.0.  I know that the hardness alkalinity and ph are not in ideal range and I have tried using ph adjusters to get it closer to ideal but just started doing this about 3 weeks ago.  No change.  After online reseach and talking to the local pet shop I started using melafix 3 months ago.  After daily dosage with weekly water changes and no results I started using melafix and pimafix together about 1 month ago.  So, after 3 total months of treatment and we have lost about 13 (approx half) of the fish.  I am at a loss as to what I should do next.  I live in a small town in rual Nebraska (we moved here from Seattle 10 months ago).  I have limited access to pet shops and mega sores with medication and advice.  I have had to rely on internet research but clearly that has not worked out.  I am open to suggestions and really hope you can help me.  Thanks!

Answer
I suspect fungus... Maybe until it gets cleared up try doing a 50% water change weekly and adding some antifungal? MarOxy I've heard is good, it supposed to also prevent fungus on eggs. You could also try jungle labs tank buddies fungus guard... What type of fish do you keep? Would they be okay with some aquarium salt? If they're tolerant of it, it will help keep some of the unwanted bacteria down and help prevent infections. I wouldn't use it until the fish with damaged tissue are healed though, I'm sure it would sting. Also you could try some water conditioner that has healing properties. I have had really good results with Stress Zyme from Aquarium Pharmaceuticals.