In my 25+ years keeping reef tanks I figured I had seen it all. Well, this can be a humbling hobby and I was reminded of this when I discovered dinos, short for dinoflagellates, in my 187 gallon tank about two years ago.  Dinoflagellates are notoriously difficult to eradicate, causing some aquarists to quit or break down and fully reboot their tanks.

Identifying Dinoflagellates

So what are dinoflagellates? There are many forms, but the kind that gives reef keepers fits is a snot-like algae substance that attaches to rocks, sand, power heads, corals and anything else they can latch on to. They are typically brown, long, stringy and have air bubbles. They can literally coat everything, and some varieties can release toxins that are especially harmful to snails. Correct identification is critical when coming up with a treatment plan, and snail die off is one key indicator that the “brown menace” (known also as dinos) is in the house.


Dinoflagellates appeared in my 187 gallon tank after I added too much coral food. I had ramped up the dosage too quickly and within a couple of weeks I started to notice a brown stringy substance on the rocks, as well as on my SPS frags. I was concerned because it caused the polyps on the frags to retract, and when I used a turkey baster to blow off the substance it returned almost immediately. Not good at all.

Failed Attempts At Eradication

What to do? One theory to rid a tank of dinoflagellates is to elevate the tank’s pH to 8.4 to 8.5. Some folks have reported success with this method, and I did try it for a bit, but had trouble maintaining my pH in that range. One drawback to consider when maintaining a high pH is that it will accelerate calcification, a potential problem since it can potentially seize up return pumps and power heads.


I then decided to try a different route. My plan was to manually remove as much of the dinoflagellates as possible, turn the lights off for three days, and dose the tank with a 3% solution of hydrogen peroxide on a daily basis. My intent was to follow a typical rule of thumb for hydrogen peroxide by dosing with 1 ml per 10 gallons of aquarium water. Hydrogen peroxide is an oxidizer and it removes electrons from the reactant that it is exposed to. In theory, when it comes in contact with algae, it breaks down, and thereby kills it off.

3 Day Blackout – A Band Aid

Did the blackout in conjunction with the hydrogen peroxide dosing eliminate the dreaded dinoflagellates? It did for a few weeks, but the dinos came back after I started to dose with the coral food again. I was dismayed to say the least, but I decided to throw more firepower at the problem. My new plan was to do another three day blackout, double the dosage of hydrogen peroxide (2 mls per 10 gallons of aquarium water), stop dosing coral food for an extended period of time, and cease and desist on water changes for 4 weeks (there is a belief that dinos can feed on certain trace elements present in salt water mixes). Did this work?  Nope.


I also tried to lower my nutrients by using GFO aggressively and skimming heavily, but the dinos seemed to get worse. Predictably, my SPS were stressed from all these unusual treatments, as well as having the dinos covering their polyps. It was apparent to me that I would lose them if things didn’t change soon, so I tried some riskier approaches.



Risky Remedies

I decided to use Vibrant Liquid Aquarium Cleaner, which is a bacterial additive meant to consume problematic algae substances, such as dinoflagellates. I hesitated before using Vibrant since I was adding additional bacteria to my tank and had no insight into how it would affect my current bacterial bed. But I was desperate, so I gave it a shot, figuring I had nothing to lose. After dosing for a couple of weeks, the dinos did recede and seemed to disappear, but this led to the nasty Spirulina cyano outbreak. Anyway, they came back.


Cyano Cyanobacteria


What to do now? Well, I had heard of some reef keepers having success using Seachem Metroplex, which apparently kept the dinoflagellates from reproducing. Despite these claims, there was no real concrete scientific evidence that this was true and that Metroplex was reef-safe. But I was at my wit’s end, so I gave it a shot. Unfortunately, after dosing Metroplex, my dinos kept spreading and I soon started to lose a lot of SPS.

The “Dirty” Method?

My last ditch effort was to go the “dirty” method and add a lot of pods to the tank, and to also raise nutrients. The theory here is that pods will help to consume dinos while additional nutrients will spur on algae growth, supposedly a plus since the algae would outcompete the dinos by consuming nutrients previously taken in by the dinos. In theory it sounds good, but in my case it didn’t work.


As I surveyed my tank with dismay, it was obvious to me that it was time to start over, since my corals had taken a lot of abuse from all the different courses of treatment. The dinos had beaten me this time, but sometimes a reboot is the best course of action.


To make sure the dinos would not return, I broke the tank down and let it sit dry for a couple of weeks. I then filled it up with RO/DI water and ran this through the filtration system for two more weeks. Two months after adding Haitian live rock, fish and corals I began to notice a familiar sight, dinoflagellates.


Many things ran through my head at that point, including disbelief, despair and confusion. How did they get back in?  Did they somehow survive the tank breakdown? Did they hitchhike in on some corals?


Natural Approach Saves The Day

It was not a very large outbreak but they were present. At that point I decided to stick to natural methods of eradication. No more blackouts, hydrogen peroxide or other chemicals. I focused on dialing in my Pax Bellum ARID algae reactor to maximize chaeto growth and out-compete the dinos. Once that was done I noticed the dinos began to retreat and eventually disappear.


Pax Bellum ARID C30


A UV Sterilizer?

I do not have any first hand knowledge but many reef keepers have reporter a lot of success using a UV sterilizer to eradicate dinos in the water column. If you want to give this method a shot you can use the AA Aquarium Green Killing Machine UV sterilizer, an inexpensive unit I have used a few times to fight bacterial blooms.

Final Thoughts

Was the reboot a waste? I don’t think so, since so much was out of whack with the tank’s critters and bacteria. I also believe the live rock helped, as it had much more biodiversity versus young dry rock.


In general, the best tactic to fight algae is to figure out the source of an algae problem before attempting to fix it. If you fail to pinpoint the problem, then problematic algae will keep coming back.

Ultimately, multiple options exist to prevent and fight nasty algae outbreaks, so it is very important for any reef keeper to be diligent, and not to despair when confronted with this type of problem. Odds are, it can be beaten. The best solution is to have a good nutrient control plan in place, and to do frequent water testing to nip any potential problems in the bud.


Algae growth is fueled by a few different elements, but only one has to be low enough to prevent growth (usually it is easiest to limit the phosphates). Most importantly, go the natural route for eradication whenever possible.



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If you would like some help with a new tank build, including help designing a custom aquarium, or help re-configuring your current setup then you can visit this page for more information. And if you are looking to add some equipment, I do sell GHL, Pax Bellum, Reef Octopus Calcium and Kalk Reactors and Royal Exclusiv products, including Dreamboxes, which is the equipment I use and recommend.


As for additional insights and information, please explore my many other reef tank and SPS related articles as well as my YouTube channel. For an even deeper dive into reef tank care you can check out my Reef Keeping Master Class. This online course is an immersive and one of a kind educational tool designed to help reef aquarium hobbyists build and maintain a beautiful SPS reef tank. The course is a series of video presentations with some supplemental video from my YouTube channel. There are also quizzes to help students retain and understand the information presented in the course.


Need some frags…..I can help with that as well 🙂 Please visit my SPS Frag store to see what is available.


Happy reef keeping!