Help me save this goldfish ? cotton fungus or bacteria?

[Laaf]

The newest pic is in a 20 gallon tank after it seems recovered and healed, except for missing most of it's tail. The earlier pics in the thread show the white cottony clumps on the tail, when it was acting sick.

I pull rocks from my pond that are covered in algae and put them in the tank. Since that pic, the fish have eaten the algae on the rocks down to stubble. About every month I have been trading out the stubble rocks for new ones covered in pond algae. I figured that was a good way to get good bacteria into the aquarium and give the fish fresh food.

 

[Laaf]

Here is the adopted friend. The algae on the rock is much eaten down from the above pic. This little fish started out solid white except for one orange eye.

My husband names the bigger fish Muckleberry Finn for it's mucky tail when we first put it in the tank.

 

[Tula]

I'm so happy to read this update! Looks like Muckleberry Finn and his friend are living the life indoors