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Q11162 - HOWTO: How to Get Rid of Red Slime (Cyanobacteria) By Robert Farnsworth, Reef Squad

How to Get Rid of Red Slime

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.


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).

Reef Tank Parameters

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
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).

EcoTech Marine VorTech Powerheads

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.

Gravel Cleaners
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 Removers


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.


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Approved Comments...
Helpful. Approved: 7/24/2014
This article should really focus more on stressing lower nutrients and the ways to achieve that. Nutrients are by far the main cause of cyano. So, the article should emphasize that and discuss things like feeding less, keeping the skimmer working efficiently, and perhaps even removing fish. Approved: 8/18/2013
Just a comment pertaining to the below comment from another reader. "The only silver lining is that if you have Apitasia, cyanobacteria will kill all of it completely." Sorry, but that is far from the truth. Recently, it has been suggested that Aiptasia and cyanobacteria can form symbiosis. Some species of Aiptasia show a clear preference for cyanobacterial mats when they settle out. Some more info can be found here: Approved: 4/21/2013
The article was thorough.. Approved: 12/17/2012
I turned off my lights for two weeks followed by water change. Worked better than any chemical. TKS TO THE PERSON WHO HAS A CORAL TANK & SUGGESTED THIS METHOD THRU FACEBOOK PAGE ;) Approved: 8/16/2012
This was a timely artole as I was slimed but I foudn a natural way to eliminate it and that was with the introduction of a Gobi (Amblygobius phalaena). Once itroduced it feeds on the substrate and filter it through its gills. This worked wonderfully. I woudl recommend this natural way to all your clients. Vic Approved: 8/12/2012
Did not tell me how medicine works or if it is safe for corals and such Approved: 5/20/2012
Informative Approved: 5/7/2012
Good Afternoon, Like forever this article is great. Best Regards, IM Approved: 5/7/2012
Good article. Will go home and put to use. Approved: 5/7/2012
My 120 gallon reef aquarium has undergone everything good and bad that can happen over the last 12 years. Cyanobacteria can definately a big problem. I was removing more than five pounds of this nasty slimy stuff every week at one point. The only silver lining is that if you have Apitasia, cyanobacteria will kill all of it completely. But this cure for Apitasia is definately worse than the disease. The root cause is almost always water quality. Be sure you are testing for alkalinity, calcium and magnesium. Over time your magnesium can reach low levels that will cause calcium to stop being produced, even with the best calcium reactor. If you normally have to scrape some corraline algae from the sides of your tank each week, then suddenly your tank sides are clear - beware, you calcium and almost certainly magnesium are getting out of whack. You wont believe how much magnesium it takes to get things back in balance again and expect a lot of dead snails. Bottom line, if your calcium, m Approved: 5/6/2012
Slime is present in every tank and maintenance is the key, even using old t5s can help the bloom. The chemiclean is miraculous. I tried all of the maintenance stuff then one treatment nailed it. I think a bubble anemome I had died which unbalanced the tank and I needed this stuff to get back in balance. Approved: 5/5/2012
I have had Red Slime and only chemical treatment made improvements. Increased water flow, proper lighting, and the best protien skimmer affordable may be your answer. I have my sump pump and 4 power heads for circulation and the only draw back is the weak swimming Clown Fish have a hard time fighting the flow. Approved: 5/5/2012
I didnt know that temps could be playing a role here. All the forums seem to push RODI and you didnt do that. Thank you! Approved: 5/4/2012
covered a wide array of fixes to the red slime problem. Approved: 5/4/2012
I have this problem and I keep getting different answers. And this article combined everyone answer I have received. I love the information that I get when these emails. Thank you so much keep them coming . Approved: 5/4/2012
I have tried all your tips and they work Approved: 5/4/2012
I have tried all your tips and they work Approved: 5/4/2012
I did not know anything about Red Slime, this was very educational. Approved: 5/4/2012
I have great luck eliminatiog red slime in my nano tank by using chemipure elite. Approved: 5/4/2012
YOU SHOULD CERTAINLY MENTION SCAVENGERS AND FISH THAT EAT THIS RED SLIME. It is a much better approach than chemicals. Animals that eat red slime can play a huge role in minimizing it before it gets out of control. Also, a large micron filter sock can keep food and other waste out of the system. Finally, although you mention phosphates, 90% of the kits sold do not accurately measure down to the low levels of nitrates that can impact a system negatively. Approved: 5/4/2012
Article Details
Created on 5/2/2012.
Last Modified on 3/26/2013.
Last Modified by Dot Yuson.
Article has been viewed 55266 times.
Rated 8 out of 10 based on 158 votes.
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