Have you ever seen the movie Ghostbusters?

Do you remember Slimer, the ugly spud-shaped ghost that left a nasty slime trail everywhere it went?

While funny in the film, having slime inside your aquarium is no laughing matter. It consumes nutrients in your water, blankets coral and creates an unsightly aquascape.

Cyanobacteria is classified as a photosynthetic organism with properties of both algae and bacteria. Usually referred to as red slime algae in the aquarium hobby, cyanobacteria can actually range in color from red and purple to black and even a brilliant green. Cyanobacteria benefits from aquarium lighting, uneaten fish food and poor aquarium maintenance habits. Once the slime spreads, it can quickly carpet your coral, substrate, live rock and even your aquarium glass or acrylic.

Cyanobacteria appears when high nutrients (phosphates, nitrates and silicate) are combined with certain light, temperature and water flow conditions.

I've been slimed. What should I do?

The first thing you want to do is test your aquarium water. Nitrate and phosphate levels are generally elevated when cyanobacteria is present.

Perform frequent water changes using nitrate and phosphate-free saltwater to get your tank parameters back in check. We generally recommend changing 10-15% of your total tank volume once per week. It is of utmost importance that the freshwater you use to mix your saltwater and top off your aquarium is also free of nitrates, phosphates and silicates.

We carry a ton of test kits you can use to monitor your water chemistry as well as various forms of filter media to help control what is present inside your aquarium. But if the water you are putting into your tank is contaminated to begin with, regularly changing your water and media will only go so far.

We highly recommend reading How to Prevent Algae in Aquarium Systems as a primer for this subject or as supplementary reading once you have completed this article. It will give you a better understanding of what causes algae and how to better control the nutrients in your tank.

Cyanobacteria thrives in lower flow environments. Your filtration system should be turning over 8 to 10 times your total tank volume per hour to help keep the water clean. Positioning your powerhead, even adding another, to increase the flow through problematic areas (aka "dead spots") will also help combat the problem. If your aquascape is stacked into a wall without any gaps, caves or crevices for water to circulate, you may eventually want to consider rearranging your rockwork into something more open (read 6 Ways to Improve Water Flow to learn more). Routinely check your protein skimmer to ensure it is operating efficiently and clean out your collection cup at least once each week (read How to Select, Setup and Maintain a Protein Skimmer for more info). 

Old light bulbs and/or improper light spectrum can also contribute to cyanobacteria and nuisance algae growth. Take note when you replace your bulbs so you can set a reminder on your phone or calendar to change them out again in 6-18 months (excluding LEDs). Avoiding heavy warm colors, like red and yellow, may help some.

This will probably be easier if you have a controller or monitoring device, but check to see what is the average temperature of your aquarium. Stability is essential and many hobbyists have reported accelerated growth in tanks where temperatures are above 80°. If appropriate for the livestock in your tank, keeping the water temperature 76° to 78° is a small adjustment that can make a big difference.

A relatively new form of filter media, biopellets, are reportedly causing red slime outbreaks in some aquariums shortly after introduction. Once the biopellets have established, the cyanobacteria recedes. If you recently set up a biopellet reactor or are planning to soon, keep in mind this is to be expected (read Setting up a Biopellet Reactor to learn best practices from our resident biopellet expert).

Maintaining proper parameters is essential to the health and well-being of fish, coral and invertebrate inside your reef aquarium. We've created this handy reference chart for you to bookmark (or share!) so you'll always know ideal parameters when performing water tests. SEE CHART

Good prevention tips, but how do I get rid of the slime I have now?

If you skipped ahead to this point, fine, but make time to read this article from the beginning later so you can correct the factors contributing to the presence of cyanobacteria in your aquarium. Cleaning and/or treating your aquarium for cyanobacteria without addressing the underlying causes will only be a temporary solution.

The good news is getting rid of red slime in your aquarium is pretty easy. It will require a little elbow grease, so grab your siphon and let's get to work.

During your weekly water change, use a gravel cleaner (or any 1/2" to 3/4" piece of vinyl tubing) to suck up as much slime as possible from your sandbed and rocks. Replace the water you have removed with clean, nitrate and phosphate-free saltwater. If your problem is persistent, a trick you can do is siphon the water out of your aquarium and then through a filter sock to trap the gunk. Then just add the filtered back into your aquarium. This will allow you to siphon until the tank is truly clean without having to worry about removing too much of your existing water. If you have a sump system with a filter sock on the drain, simply siphon from your display, placing the other end of tubing into the filter sock. Once you have siphoned out all of the bacteria, replace the filter stock immediately with a clean one.

Chemical treatments are a very effective way to remove cyanobacteria. They do not, however, prevent it from coming back. Straighten out any nutrient, water flow, temperature or lighting issues that could be causing the outbreak before administering any chemical treatments. This will help ensure if you do decide to use chemical remover, it will successfully eliminate the problem. Besides, you may not even need a chemical treatment after making adjustments to your tank and maintenance routine. 

We carry several different cyanobacteria removers, the most popular being Boyd Chemiclean, followed by Ultralife Red Slime Remover and Aqua Vision Aquatics Cyano Solution. Although all three of the aforementioned products state they are reef safe, be sure to follow the manufacturer's instructions to a tee. Most require that you turn off your protein skimmer and remove carbon during treatment.

It is important to use an air stone during treatment to ensure ample oxygen is available while your tank is being medicated. Once the treatment is complete, it is a good idea to perform a 10% water change and turn on your protein skimmer. This will help to remove any residual medication from the water column. We are speaking in generalities, of course, so again please heed the manufacturer's instructions closely when using any chemical treatment.


Red slime is one of the most common problems plaguing marine aquariums. Fortunately for aquarium hobbyists, it is also one of the easiest to control and treat. If you still have questions, we gotta ask: who you gonna call? You can reach our aquarium experts at 1-800-566-FISH (3474) or send us a message anytime. If you won the war against cyanobacteria in your aquarium, please share your experiences with us and other readers in a comment below.