For years, well really nearly 3 decades, my father and I have been raising tropical freshwater fish. Occasionally the tank will somehow acquire a growth of black algae.
Black algae is insidious. Once you get it it is impossible to get rid of without tearing the tank apart and bleaching everything. The danger here is that bleach is highly toxic to fish. Even a single drop can kill off an entire 120 gallon tank full of fish.
Maybe the most popularly debated topic online is how to get rid of black algae, and until now nothing has worked.
I accidentally ran across the answer over a month ago!!! Here it is:
My heater (~16 years old!) failed and failed on. The temperature in the tank spiked to 110F before I noticed.
Over the weeks the tank, which previously was completely covered with black algae, has cleared up. Even the normal green algae is gone!
I do not recommend getting your tank that hot with the fish in it. All but 2 of my fish died :(. You can put them in a temporary holding tank, or buckets, while you heat up the tank.
I am curious to know of anyone else out there who has tried this method and how it worked for you.
Edit (Feb 2017): Noting from a commenter- My tank did not have any live plants in it. They are all plastic.
Here are a couple pics of my tank today. I wish I had a before pic to show you, even the plants were covered in the black algae.