Get Rid Of Cyanobacteria Or Red Slime Algae Forever!

Just like our previous episode all about eradicating algae, many of you landed here because you have a frustrating outbreak of red, brown, purple or even green slimy stuff in your tank. Our plan is to help you identify the problem, bust the myths and give you a solid foundation for removing and preventing this scourge for good.


Cyano or Dinos?

The red slime in your tank could be either cyanobacteria or dinoflagellates. They do look pretty similar to the untrained eye and correctly identifying the problem is critical to solving it. Let’s be honest, differentiating a bacteria and protozoa is not so simple.


In general, cyano or cyanobacteria is red colored and can be stringy or a slime that coats surfaces. Dinos often tend to be brown, snot-like in appearance with lots of bubbles attached.

Cyano is by far the most common and our advice to new reefers who are having a hard time identifying the difference is to treat it like it is cyano because it is the easiest to treat. If that doesn't work, progress on like it is dinoflagellates.

Ryan's Tank with Cyanobacteria

The New Approach to Cyanobacteria

In the past, almost all of the conversation around cyano was related to nutrients like nitrate, phosphate and poor maintenance fueling these slimes. Not because there is a lot of evidence suggesting that but more so because it sounded plausible.

While we do see cyano more often in poorly maintained tanks, our experience here at BRS tells us that elevated nitrate or phosphate is not a direct cause of cyanobacteria outbreaks. We have seen hundreds of tanks with both high and low nutrient levels experiencing cyano problems. Also, lowering nutrient levels has never proven to be an effective cure for cyano and so this debate is going to be of minimal value.

Ryan's Tank without Cyano

A better way to look at this is that a well maintained and stable reef aquarium with reasonable nitrate and phosphate levels as a result is sometimes a solution on its own. It is less about chasing a number here and more about an overall approach to good aquarium husbandry and water quality.

Step #1 - Back To Basics

Follow the general good maintenance practices we outlined in this series and wait it out. Often the issue will just go away on its own. Good maintenance primarily means keeping the rock surfaces clean as well as reasonable feeding habits. This also means keep the skimmer running optimally and do your water changes.

Hanna Instruments Phosphorus Checker

This is also a good time to test nitrate and phosphate and make sure they are not off the charts. In the event your nutrient levels are through the roof, you should first get those under control for a variety of reasons.

This is not a good time to start experimenting. Rely on good ol’ fashion water changes; 3 -4 exchanges in the amount of 30% your total tank volume evenly spaced over the following two weeks.

Protein Skimmer

If the nitrate and phosphate are absolute zero, that can also cause issues. Start feeding more or reduce filtration like reducing the lighting period on your refugium or tune down the skimmer to collect less waste until you start to get a nitrate or phosphate reading with your test kits. Even the slightest amount of nutrients are sufficient, essentially anything above zero is suitable.

Adding a powerhead to a reef tank

The only addition to the system we recommend at this point is additional powerheads because the additional flow is generally always good for the tank. It helps eliminate dead spots and flushes that surface film.

Waiting it out is obviously a better option if the slime isn't bothering any corals or harming anything. Just give it time and see how your increased approach to maintenance goes.

Dosing Brightwell Aquatics MicroBacter 7

Step #2 - Bacteria

Step #2 comes into play if your better maintenance approach had minimal to no effect yet the cyano is still within reason and not yet “out of control”. Dose competing organisms in the way of bacteria additives such as:

It’s hard to definitively share the exact mechanism of how the heterotrophic bacteria in these products work to beat cyano. Some are believed to out scavenge nutrition, likely outcompete cyano for surface area or territory and some may even be aggressive enough to consume the cyanobacteria.

Dr. Tim's Waste Away

When you use these types of competitive products you need to understand it took months for the cyano to outcompete organisms in the tank and become the problem that it is. That means it is going to take a couple of months for the bacteria to outcompete the cyano and win back the tank. Nothing good happens fast in a reef tank so have some patience, dose as directed on the bottle and let bacteria do its work.

Step #3 - Chemical Solutions

If you have what amounts to a cyano outbreak which is actively killing corals or you just can't handle looking at it any longer, our best advice is to use something like Boyd Enterprises Chemi-Clean or Ultralife Red Slime Remover.

Red Slime Remover

Chemiclean is often treated as a last resort or bandaid for an underlying problem but if you have already followed step one with a solid maintenance plan for your tank, these types of treatment can be like a reset button that gets things back on track.

When used as directed on an otherwise healthy tank they can remove the cyano quickly, usually with one or two treatments. While there is some risk when dosing anything to the tank, negative results with the red slime removers are exceedingly rare.

Cyanobacteria on rock

Don’t be surprised if the cyano comes back over time. If it does, try all three with a good maintenance plan, dosing bacteria and a red slime remover product. All of this together should not allow any room for cyano to grow inside your aquarium.

What’s Next

In the case it does not go away, it may very well be the stubborn dinoflagellates which just so happens to be the topic of our next episode in the 5 Minute Saltwater Aquarium Guide.

5 Minute Saltwater Aquarium Guide Episode #27

Looking for a different topic or have questions? You can binge the entire 5 Minute Saltwater Aquarium Guide playlist right here on our website. We also invite you to join the #askBRStv Facebook Group which is a free resource for you to ask questions, get advice, interact with other hobbyists and get your daily reef aquarium fix.

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