| Re: brown algea dropsy and skin!
Dropsy is a symptom, not a disease. It could be bacterial, fungal, a tumor, but definitely interferes with kidney and osmoregulation functions. It is not commonly spread to other healthy fish, but isolation of the sick fish is always recommended.
The causes of the symptom "Dropsy" are many, but poor water or tank conditions are at the top of the list.
An accurate diagnosis of "Dropsy" is very difficult and once the disease process has progressed to the bloated swelling stage, internal damage probably will not be overcome.
A general tonic of 1/8 tsp. per five gallons of Epsom Salt will help relieve the bloating pressure.
Never use NaCll (table or aquarium salt)
Food soaked in Eruthromycin may help if the cause is bacterial.
The major problem is unless the causes are treated early the fish will probably not recover.
The question on water changes and water parameters is a little wacky, If you have a cycled tank with fish, your Nitrates are not going to be 0. You might want to revisit your tests.
Water changes are not going to help you much with the algae. Can you post a pic so we can see what is going on and help you out there?
Regards,
Jay | 
