well, the fuzzies are fungus, but do they have it while they're alive? as far as i know, the salt should take care of that. I'm not entirely sure, but it sounds like you should try checking your ammonia levels. pH too.

 

First thing - "Do as you oughta - change the water!!"

What are your water parameters? Especially Ammonia, Nitrite and Nitrate? If you don't know them - then I STRONGLY suggest a partial water change - up to 40 or 50 percent - using fresh DECHLORINATED water that is the right temperature (same temp as the water currently in the tank)! Personally, I like to use Prime as a dechlorinator - it will also help with Ammonia/Nitrite/and or nitrate toxicity! Follow the directions - Prime is more concentrated than most dechlorinators! Then get your water tested! Ammonia and Nitrites should be ZERO and NitrATES should be less than 20! Do you know if your tank has 'cycled' yet? (look up "Nitrogen Cycle in aquarium" here or elsewhere on the web if you don't know what I'm talking about) If it hasn't cycled yet, a bacterial product like Stability or Cycle could help somewhat but everything comes down to FRESH CLEAN water!!! Water quality is the key to fish health!

 

MKM pretty much said everything(well, i might add).The rotting food creates ammoni in the water, so I would keep your tank clean. Feed less, or in a way that more food is eaten, and also ( if you havent already) invest in a gravel vacuum. Some scavengers might also help eat uneaten food.

 

You did a full water change? As in you changed all of the water at once?
I think that's probably no small part of your problem. Never do that.
Oh well, you can't go back and undo it now, so now just treat the symptoms.
MelaFix, PimaFix, 1 teaspoon of salt per five gallons, and some "Safe Start" or 'Stability" should help get things back under control.

 

Never do a full water change?

 

When you change out all of your water, you basically start your cycle over, and when there's fish in the tank, that could be fatal. It is recommended changing 25-30% of your water weekly, along with gravel vacs

 

When you change out all of your water, you basically start your cycle over...

What do you mean by this?

 

Meaning the water, more specifically the gravel and filter media, contain a lot of the beneficial bacteria that an aquarium basically runs off of. By changing out all of the water, you do several things.

1. You lose a lot of the beneficial bacteria, and it may not be able to fully handle the bioload until they rebuild. This will cause ammonia spikes and nitrite spikes, which could burn the gills of and even kill your fish.

2. You can in theory get away with doing daily 100% water changes, but that leads to even more risk because of changes in water parameters, such as temperature, pH, alkalinity, chlorine levels in the water, hardness, etc. It can be done, but it is very dangerous, very tedious, and overall a bad idea.

 

As long as the gravel and media( where most bacteria is) doesnt dry out, I dont see how your cycle would restart. Unless you mean that it would die as a result of now Ammonia, nitrate and nitrite, but then you wouldnt have to worry about having bacteria since they would be zero( assuming you keep doing 100% WC's). But I do agree that 100% WC's have the potential to shock your fish due to different water parameters.