I haven't really had any trouble with my adf's but I have heard that they do have issues with the acidity of the water, is their a chance your water could have had a
pH drop? Or the white fuzz could have been a fungus? I am honestly at a loss, the only way I have lost adf's is the pair I had 2 years before this pair escaped and died on the floor of my boys room. (and I am saying I must be lucky to had them as long as I did then because at that time I didn't know anything about checking water parameters and I was very lazy about upkeep on the aquarium).