Why Do I Have Black Algae in My Fish Tank?

The term black algae is ironic, seeing as it's actually a type of cyano-bacteria -- not an algae at all! Generally, it begins to grow in your fish tank for one of several reasons -- either the nitrate or phosphate levels are too high, or you are leaving the light on too long.

Because it begins to form layers as it ages, it can be one of the most difficult Fish Problems to overcome in the aquaria.

Black algae can quickly become a nuisance, especially to the new aquarist. Here are a few tips to help you get rid of it!

1. Do a water change.

One of the first things you should do if you are having black algae growth in your fish tank is to perform a water test. Specifically check the nitrate (and phosphate if possible) reading to see if it is abnormally high. If any of the results are problematic, conduct a large water change. This will help you bring your levels back down to acceptable parameters -- you may have to continue this for several days.

2. Turn out the lights.

One of the most common reasons that aquarists encounter black algae is because they leave the lights on for too long. Try to keep them on for no longer than 12 hours per day -- less is fine as long as you don't have live plants growing. Initially, leave them off for several days and see if the fuzzy growths begin to subside. Remember, your fish tank is not meant to be a night light!

3. Scrub it off.

As long as you remain persistent in your efforts, it is entirely possible to scrub the black algae off of the decorations and glass. Just remember that you have to keep at it for a while since it grows in layers -- most people continue to have reoccurring black patches because they only take the time to scrub off the first layer.

While it can be a pretty disturbing phenomenon when you are new to keeping fish, just remember that black algae is not impossible to rid yourself of. Take a minute to relax, and then start playing detective. If you learn how to pay attention to its signs, your fish tank is pretty good about leaving you clues indicating that something is wrong. It is very important to get to the bottom of WHY the black algae is growing in the first place before you can ever hope to get rid of it.