How to Identify and Eliminate Dinoflagellates (Dinos) in Reef Aquariums

Your tank is riddled in brown or red bubbly slime and it's covering all your rock work, sand and corals. Everything looks miserable. Welcome to a nearly unavoidable part of reef keeping. Unfortunately, you probably have dinoflagellates, more commonly known as dinos in the reefing community. Dinoflagellates are a single celled eukaryotic algae that, despite the issues they cause, play a vital role in the form of a primary producer at the foundation of the ecological food chain. With over 2000 species of dinoflagellates, they have a multitude of different attributes, benefits, and unfortunate side effects (to put it lightly). One of the better attributes of dinoflagellates is the symbiotic relationship formed with many beloved marine animals. And yes, this includes coral!

This single cell organism is part of who we have to thank for all the amazing corals we get to keep in our aquariums! By forming a symbiotic relationship with coral the dinoflagellate provides energy to the coral in the form of lipids, amino acids, and sugars while the dinoflagellates get protection from predators by dwelling "inside" the corals. [1]Now this may sound exactly like another relationship we know of between coral and another algae. This is because the zooxanthellae we know and love are actually a genus of dinoflagellate!

How did I get Dinos?

 

Diatoms (“pizza slices”). Dinoflagellates (multiple species,brown circles)

Dinoflagellates are an important part of the reef ecosystem and vital to coral health. The issues arise when the ideal conditions are met and they overpopulate the tank. This often causes a brown or red bubbly slime in our tanks or what is called the "red tide" in nature[2]. This can happen when nutrients in the water drop resulting in many of the beneficial bacteria species that live within our reef tanks to experience a die off. In turn, the dinoflagellates which were previously suppressed due to the other bacteria populations, take this opportunity to establish a stronger presence in the tank. Their numbers explode as they don't require the same amount of nutrients as other beneficial species. Dinoflagellates also have the advantage of being able to create energy through photosynthesis[3,4].

Identifying Dinoflagellates

 

In the home reef tank, there are 4 main species we deal with: Amphidinium, Coolia, Prorocentrum, and Ostreopsis. Each comes with their own challenges and specific way of combatting them. Therefore, it is an important step to identify which species of dinoflagellate(s) you have before starting treatment. This can be done through a simple microscope. In the event that you do not own your own, you can always bring in a sample of the slime to New Dawn and we can take a look to help you identify them.

Step 1: Why are dinos taking over my tank?

Outside of which type of dinoflagellates you have, the ‘why’ or ‘how’ is the second most important step. Sadly there can be multiple issues going on at once that can contribute to their rise in population. Generally it isn’t just one thing that contributes to their rise but here are the reasons we typically see at New Dawn:

• There has been-or currently is- an imbalance in your tank. The ratio between nitrates and phosphates is vital not only to coral health, but in maintaining other types of algae and bacteria. Low or no nutrients can result in the beneficial microfauna dying off. This leaves behind bare surfaces where the dinoflagellates were able to take hold.
• There were not enough types of beneficial bacteria to keep the dinoflagellates at bay.
• Too high of nitrates or phosphates can also cause microfauna to die off or feed “bad” bacteria.
• Too low of nitrates or phosphates can starve beneficial microfauna while other “bad” algae or bacteria like cyanobacteria or dinoflagellates can more reliably convert to photosynthesis.

Step 2: How do I get rid of dinos?

Tools to help with dinoflagellate management and removal.

Testing your water parameters(or getting them tested here at New Dawn) and determining whether you have high or low nutrients, or even a mix of both, is important to determine what the next steps will be.

If you are dealing with a lack of nutrients or bottoming out one or both parameters, this is most likely caused by the diet of the dinoflagellates. They have food preferences(nitrates or phosphates) just as we do! Additionally, if one parameter is or was high and the other low, this can be a cause for dysfunction (and dinoflagellates) to take hold in the tank. High nutrients can also be a cause, as this provides excess food for "bad" bacteria and algae. Generally water parameters should fall within these ranges:

• Nitrates should test between 10-20 ppm.
  • If the nitrate test comes back lower than 30ppm’s, this is not something to worry about and should be taken care of after the dino treatment is complete. We want as many nutrients in the tank for the other beneficial bacteria as possible without harming coral, fish and invertebrates. Use Nitrify to bring nitrate back into the target range during treatment.
  • If the nitrate test results in a 0 or near 0 ppm, they will need to be boosted into the ideal range to allow beneficial microfauna to uptake them as nutrients. Nitrify by Reef Charge is an ideal product for this. Dose 1 mL of Nitrify per gallon of tank water to increase the nitrates by ~8 ppm. Test your water the day after dosing and adjust doses accordingly. Nitrate readings should stay above 10 ppm the entire treatment period.
• Phosphates should test between 0.05 - 0.15 ppm
  • If the phosphate test comes back in a high range, it is not something to worry about and should be taken care of after the dino treatment is completed. Unless it’s at or above 0.40ppm as this can suffocate invertebrates, some types of coral and some species of fish.
  • If the phosphate test results in 0 or near 0 ppm, they will need to be boosted into the ideal range. Phosphorize by Reef Charge is an ideal product for this. Dose 1 mL of Phosphorize per gallon of tank water to increase the phosphates by ~0.3 ppm. Test your water the day after dosing and adjust doses accordingly. Phosphate readings should stay above 0.05 ppm the entire treatment period. Stabilize phosphate to support beneficial competitors.

  Another important note: stop all water changes during the treatment period. Unless nitrates and phosphates are actively causing harm to your tank, you want as many nutrients as possible for everyone in the tank. That includes your corals! Additionally, this will help to stabilize the nutrients in the tank in the long run.

  It is recommended you blow away any dinos laying on coral daily to help prevent coral deaths and recessions. Dinoflagellates will cause coral flesh to retract or burn off, so unfortunately some loss is to be expected.

  Step 3: Intra and Interspecies Competition.
  

  

  Now that we have created ideal conditions for the dinoflagellates competition, we will utilize other microfauna to attack and outcompete the dinoflagellates. Some of the microfauna will occur naturally in your system, which is why it is important to get your nutrients up! Attacking dinos is the hardest part of this procedure, each species requires unique methods to diminish their populations as they all have different methods of populating your tanks.

  Method 1: Copepod and phytoplankton (broadly effective)

  This method relies on pods- more specifically Tigriopus copepods- and Rhodomonas phytoplankton. The idea behind this method is to dose your tanks with something that will "eat" the dinoflagellates. Tigriopus copepods (fortunately for us), have a diet that includes dinoflagellates! Therefore they can be used as a preventative measure and solution. By dosing your tank with Tigriopus and supplementing them with Rhodomonas, you can increase the copepod population in the tank and have your very own group of dino busters! However, these little guys can only do so much. This method should be accompanied by any of the following methods to increase your success of getting rid of the dinoflagellates.

  

  Method 2: Silicate dosing

  For species such as Amphidinium (Large & Small) and Prorocentrum we need a way to attack them while they are visible and in hiding. These types of dinos will typically be the hardest to remove as they retreat in the sand-bed once the lights are off and are not free floating like other species. Therefore, we need a way to attack them in the sand. To do this, we are looking to create a bloom of other beneficial bacteria to outcompete and suffocate them. Diatoms are fast growing and will inhabit the sand and rock and outcompete the dinoflagellates.

  

  Silicate-supported diatoms can occupy sand/rock and outcompete sand-dwelling dinos.

  To induce a diatom bloom we are looking to increase the silicates in the tank— for this we recommend Silicate14+ by Reef Charge. Start at 3 mL per 10 gallons until you notice muddy flakes covering your tank instead of slimy bubbles. This indicates a diatom bloom and are headed in the right direction! You will have to dose for a bit longer than expected, as Dino resurgence is very common.

  We recommend to continue dosing silicates for 2 weeks past the disappearance of the dinos. Then proceed to dose 1 mL per 10 gallon to maintain the diatoms for another week before stopping. Once treatment is over, silicates will be consumed by sponges and diatoms, which will lead to a depletion of silicates and get rid of the diatom bloom.

  Method 3: UV sterilizer

  Ostreopsis and Coolia are free floating during the night, making them significantly easier to get rid of. While they are easier to deal with, they are capable of releasing toxins harmful to most invertebrates. As a result, you may sadly see some of your clean up crew disappear. The most efficient method of getting rid of any free floating microbes in your tank, including dinos, is by using a UV. In this instance, an oversized UV is the best way to go to ensure that all of the water is getting sterilized. Typically we measure/calculate it out as follows: 1 watt per 3 gallons which would run at 1-3 gph x tank volume. If possible, the most effective method would be plumbing the UV directly into the display.

  Method 4: Hydrogen Peroxide

  Hydrogen peroxide dosing has also proved to be adequate in the fight against the free floating dinos(ostreopsis and coolia). For this, you need 3% hydrogen peroxide and to dosing 1 mL per 10 gallons every 24h. This dosing should happen after the lights are out, once the dinos have gone into a free floating state.

  Method 5: The kitchen sink.

  All of these attack methods can be used at the same time. It is possible, and more than likely, that the tank is infested with multiple species of dinoflagellates. Therefore, we may recommend one treatment to start, or multiple. It all depends on what we see under the scope!

  What to avoid.

  A common myth is that black outs are a sure way of getting rid of dinos. This should be avoided at all costs. In blackout conditions, dinoflagellates will go into a cyst form and lay dormant for months, resulting in a false win over the dinoflagellates. Once the blackout period is over, they will return from their dormant state to take over your tank once again.

  STEP 4: More competition and replenishing your tank.

  Now that we have created ideal conditions for the competition, attacked the dinoflagellates, we face bare surfaces. ideal for opportunistic dinos to colonize. To prevent this, we need to seed these surfaces in the tank with beneficial bacteria to help combat any future outbreaks.

  For this, we recommend Planktura's Bacto Fuel - Palustris live bacteria. This live bacteria will help colonize your rock, sand and glass surfaces creating a biofilm and competing for nutrients. It is important to reseed your tank with beneficial bacteria, as the numbers may have diminished with all of the treatment, or just to create more competition.

  
  

  

  Final comments.

  It is important to remember all of these steps need to happen at the same time. As you are creating ideal conditions for the competitors, you attack the dinos and replace them as soon as possible. For the easier strains, such as Ostreopsis and Coolia, this could be resolved in a matter of weeks, but with the harder strains this could be a 2-3 month long battle but don't give up!

  This is why we recommend you continue your treatments for up to 2 weeks after all of the dinos have been cleared to ensure they won’t come back. After this 2 week period, you can resume your normal maintenance and keep an eye on your nutrients to prevent any future outbreaks. This should not discourage any new reefers as anyone who has been in this hobby has experienced dinos more than once! Eventually we all make it through and our tanks return to what they once were. Here at New Dawn Aquaculture, we have your back. Feel free to come visit us anytime for help with your dino problems and we will do our best to assist you.

  Sources:

  [1] E. A. Hambleton, “How corals get their nutrients,” eLife, https://pmc.ncbi.nlm.nih.gov/articles/PMC10438905/ (accessed Nov. 4, 2025).
  [2] “Dinoflagellate,” Smithsonian Ocean, https://ocean.si.edu/ocean-life/plankton/dinoflagellate (accessed Nov. 4, 2025).
  [3] Dinoflagellate - an overview | sciencedirect topics, https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dinoflagellate (accessed Nov. 5, 2025).
  [4] Y. Bi, F. Wang, and W. Zhang, “OMICS analysis for Dinoflagellates Biology Research,” Microorganisms, https://pmc.ncbi.nlm.nih.gov/articles/PMC6780300/ (accessed Nov. 4, 2025).

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  Related Products

  

  Dino Buster Bundle

  A curated bundle to support nutrient balance and competition during dino management.

  

  Palustris – Bacto Fuel

  Live bacteria to reseed rock, sand, and glass after treatment.

  

  Tigriopus – Reef Pulse

  Large copepods that graze on dinos and boost biodiversity.

  

  Reef Charge Nitrify

  Raise nitrate into the ideal range during treatment.

  

  Reef Charge Phosphorize

  Stabilize phosphate to prevent dinos from gaining an edge.

  

  Reef Charge Silicate14+

  Encourage diatoms to outcompete sand-dwelling dinos.