How To Get Rid Of Dinoflagellates

How To Get Rid Of Dinoflagellates

How To Get Rid Of Dinoflagellates


So you have dinos.  The dreaded upside-down brown snot with air bubbles attached to the end.  Maybe it started slowly with a few snails dying, but then accelerated quickly and is even irritating your corals.  Who knows, maybe a fish or two died after trying a bite.

What can you do?  You head to the internet, and get dazzled by hundreds of threads, blogs, and videos, telling you what has and hasn’t worked.  After a couple hours of research, you slam the computer shut or throw your hands up in despair, because you are no closer to an answer then when you began!

I know that feeling, believe you me!  I have dealt with dinoflagellates multiple times, and each time found success in different ways.

Here’s the problem.  There is no consensus in the saltwater aquarium hobby as to why dinoflagellates show up in your tank and/or how to treat them. And on top of that, even as recently as 2018, we thought high nitrates and phosphates were a contributing factor, and today we believe the exact opposite!

If you have felt frustrated and want to give up, then this blog is for you.  In four sections we are going to arm you with the knowledge and motivation you need to take control and beat dinos.

This is not a quick fix.  It probably took 2-3 months of poor husbandry for the dinoflagellates to appear, and it will take as long for them to disappear.

But have heart! You can and will defeat this foe!  Check out the video I made all about my anti-dinoflagellate battle plan. I promise you will have a better understanding of the why and how after this short blog! Best of luck, and don’t stop until you emerge victorious!

What Are Dinoflagellates

© 2017 Encyclopedia Britannica

Rather than me summarizing, here it is direct from Wikipedia: Click here for the original article

  • The dinoflagellates (Greek δῖνος dinos “whirling” and Latin flagellum “whip, scourge”) are single-celled eukaryotes constituting the phylum Dinoflagellata.[5] Usually considered algae, dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations are distributed depending on sea surface temperaturesalinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy and myzocytosis).[6][7]
  • About 1,555 species of free-living marine dinoflagellates are currently described.[11] Another estimate suggests about 2,000 living species, of which more than 1,700 are marine (free-living, as well as benthic) and about 220 are from fresh water.[12] The latest estimates suggest a total of 2,294 living dinoflagellate species, which includes marine, freshwater, and parasitic dinoflagellates.[2]
  • A rapid accumulation of certain dinoflagellates can result in a visible coloration of the water, colloquially known as red tide (a harmful algal bloom), which can cause shellfish poisoning if humans eat contaminated shellfish. Some dinoflagellates also exhibit bioluminescence—primarily emitting blue-green light. Thus, some parts of the Indian Ocean light up at night giving blue-green light.

How To Identify Dinoflagellates In Your Tank

Description– It looks like gravity defying brown snot with an air bubble attached to the end.  You will know you have dinos if your snails/crabs start to mysteriously die.  Dinos are toxic to invertebrates, and dreaded in the hobby.

Really, the only way to positively identify dinoflagellates is through use of a microscope.

The two images above show the striking difference between diatoms and dinoflagellates.  These two types of algae are commonly  mistaken for each other by beginners.  The dead giveaway, without use of a microscope, is that dinoflagellates often if not always have an air bubble attached to them, pulling the algae up toward the surface, like an underwater stalagmite.


Why Dinoflagellates Appear In Your Tank

In 2015 I made a video, a terrible video mind you, all about dinoflagellates.  I stated that I couldn’t figure out why I had dinos because my phosphates and nitrates were at zero! Here’s the link to that video, which has been watched too many times in my opinion!

Fast forward to 2021, and now we have more anecdotal evidence that dinoflagellates thrive in low nutrient environments.  So when I thought having zero phosphates and zero nitrates were a good thing, come to find out I was wrong!

So the gist of why dinos appear is this: when nitrates and phosphates drop too low, the beneficial bacteria population plummets. When that happens, dinoflagellates start to outcompete the beneficial bacteria for the remaining resources, and slowly take over.

But here is the more detailed explanation.

1. Too much filtration

I’m primarily talking about mechanical filtration here.  Although, as you’ll see below, chemical and biological filtration also come into play.

In an effort to keep our tanks clean and the water crystal clear, we rely on mechanical filtration to remove particulate matter.  Filter socks, filter floss, poly-filters, sponges, and of course protein skimmers are the prime examples.

I didn’t realize for the longest time, that you can over protein skim your water! In order to have nitrates in your water column, you need a small amount of matter to decay.  That decay becomes ammonia, which becomes nitrite, which then becomes nitrate.  And nitrate is super important, not only to keep dinos at bay, but also for coral growth and coloration.

So if your nitrates are reading zero, consider taking these two steps:

  • Change your filter sock/sponge less frequently
  • Cut back on protein skimmer use.  If you currently run your skimmer 24/7, put it on a timer instead and run it for 16 hours.  then keep adjusting the time as necessary.

Oh, and you will have to test every single day to make this happen!

2. Too little nitrate and phosphate

If the anecdotal evidence is correct, zero nitrates and zero phosphates is a perfect recipe for dinos to take over. But how do nutrients even get that low? Here are a few common causes

  • Over filtration via filter socks and protein skimmers
  • A large refugium with macroalgae that consumes all available phosphate
  • Use of media reactors with some sort of GFO
  • Excessive biological filtration with a biopellet reactor
  • Not feeding enough

3. Not enough beneficial bacteria

This one is 100% anecdotal, because we have no way to know what the concentration levels of beneficial bacteria are in our systems. What hobbyists have noticed over the years is that as phosphates and nitrates remain near zero for extended periods of time, dinos appear. So why would that be?

Well, beneficial bacteria, the bacteria that powers the nitrogen cycle, needs food to thrive.  So what is food for beneficial bacteria?  Some consume rotting fish food and waste. Other’s consume ammonia, nitrite, and nitrate. So if there is not enough of any of these, the populations of beneficial bacteria will decline.

The theory goes, that if the beneficial bacteria concentration drops too low (whatever that means), other types of bacterias/algae can start to outcompete for the same resources. Thus, cyanobacteria and dinoflagellates may just be better scavengers when the food gets tight.  And as their populations grow, they can take over a tank.

© Marine Depot

4. Too much light

With some estimates of over 2,000 dinoflagellate species, the majority if not the totality of dinos we see in saltwater aquariums, are photosynthetic.  And some species we see are extremely photosynthetic to the point where every morning your tank will look dino free but every evening it will be covered!

In my experience, too much light by itself doesn’t lead to a dino outbreak.  Anytime I have too much par for too long of a photo period, I have green hair algae or turf algae outbreaks.  But once dinos start their slow climb to ascendency in your tank, light plays a role.

If you are having algae problems of any kind, it is always a good idea to do three things:

  • Reduce the overall photoperiod.  Go from 10 hours a day to 6 hours a day.
  • Turn off your green and red LED lights if you can.
  • Reduce the light intensity by half if possible.

Reducing the intensity and length of your lights will not solve the dino outbreak by itself, but it can help you start to get a handle on the issue.

5. Not enough feeding

What is the easiest way to increase your nitrates and phosphates?  Feed more!  Most of us actually overfeed our tanks.  This can lead to high phosphates especially, which can fuel nuisance algae growth. But a minority of us (including myself), are so paranoid about nuisance algae, that we underfeed.

The reality is if you feed more, phosphates will rise faster than nitrates, and that is not ideal.  So how do you combat this problem?

  • Feed more frozen foods which are less nutrient dense.
  • Consider setting up a macroalgae refugium to help consume phosphates.
  • Or just don’t worry about it and be okay with slightly higher phosphate levels!

So if you’re nitrate and phosphates are near zero, the first step is to increase feeding amount/frequency!

How To Get Rid Of Dinoflagellates In Your Saltwater Aquarium

Before we go into detail, here is the basic recipe

  • Maintain NO3 (nitrates) between 3-5 ppm
  • Maintain PO4 (phosphates) between 0.07-0.15 ppm
  • Remove dinoflagellates everyday
  • Dose beneficial bacteria
  • Lower photoperiod and intensity of lights
  • Raise water temperature to 81-82 degrees F
  • Consider adding a UV sterilizer

There is no widely accepted recipe for success on how to get rid of dinoflagellates. But don’t lose hope!  While the hobby might not have a sure-fire solution, there are strategies that seem to work.

Here is the rub though: It took your tank weeks if not months to develop a dinoflagellate outbreak.  It will take you weeks if not months to beat dinos.  If you are unwilling to battle dinos everyday for up to a few months, then give up now because the dinos will win.

We’re not saying you have to spend several hours a day.  But you will likely need to devote about 15 minutes each and every day toward your dino battle.

And not only that, you have to keep your spirits up!  Fighting dinos is a frustratingly long game with roadblocks and setbacks throughout.  But, if you follow our recipe for success, and you refuse to give up, we believe you will win.

By the way, the recipe below is all about removing dinos, increasing beneficial bacteria, and keeping your NO3 (nitrate) and PO4 (phosphate) elevated.  You may pick and choose whether you want to feed more, dose, or filter less as your primary means of increasing nutrients.

1. Test Nitrates & Phosphates Daily

Test nitrates and phosphates at the same time everyday.  The two test kits above are by far my favorites for testing NO3 and PO4.

You need to understand the trends of your tank. If your nitrates and phosphates are low, then you will need to take steps to increase those parameters via dosing, feeding, or less filtering.

Dinos seem to appear after prolonged periods of zero/near-zero phosphates & nitrates, so do whatever you need to using the steps below to keep those parameters slightly elevated.

During this battle, error on the side of slightly too much NO3 and PO4 rather than too little.

2. Maintain Phosphates Between 0.08-0.15ppm and Nitrates Between 3-5ppm

There are so many different ways to do this from feeding more to filtering less.  But if you don’t want to use either of these methods, there is a third option.

Purchase NO3 and PO4 in a bottle, and dose daily. There are several products out there for doing this, but understand that you will need to test and dose daily for this to work.

The benefits of dosing NO3 and PO4 directly, is you don’t have to worry about fiddling with filtration and feeding.  Because let’s be honest.  Oftentimes when we feed more, our phosphates go up faster than our nitrates, and we get nuisance algae growth.

And on the flip side, if we start filtering less, we could see a sudden surge in NO3 and PO4, which may be difficult to reduce later.

So whatever method(s) you choose to keeping nitrates (NO3) and phosphates (PO4) slightly elevated, be vigilant and adjust daily as needed.

And if you are struggling with other types of nuisance algae, be sure to check out our “Beginner’s Guide to Nuisance Algae.”

3. Use Mechanical Filtration Less

So this can get a bit confusing.  Here’s what I mean.  If you just tested your PO4 and NO3 and found them near zero, AND you don’t have any dinoflagellates, then yes, reducing your mechanical filtration can help prevent dinos.  Why is that? Because either changing your filter socks less or not running your protein skimmer all the time will eventually lead to increased PO4 and NO3 (as long as other factors remain constant). But, and here is the big BUT…

If you already have dinos, then you will want to change out your filter socks/sponges/filter floss every morning to remove dinos. You can still run your protein skimmer less to help increase nutrient levels. But at least for filter socks/sponges/floss, daily replacements will help remove dinos from your system.

If you run your protein skimmer 24/7, you may be pulling too many nutrients out of the water column.  How does your skimmate look?  Is it light brown in color? If so, you have what is called a “wet” skim, meaning there is more water than organic material.  And a “wet” skim may be a sign that you are pulling too many nutrients out of the water column.

So if your nitrates are at zero, consider either putting your skimmer on a timer and running it 12 hours a day, or consider adjusting the water level in the skimmer body itself to produce a more “dry” skim.

4. Feed More

The easiest way to increase phosphates and nitrates is just to feed more.  That usually means increasing the frequency of feeding.  If you feed twice a day, try three times a day.  If that doesn’t help go to four times each day.  As long as you are tracking your NO3 and PO4 levels daily, you will know when it is time to increase feeding or cut back.

Just a quick note of pellet/flake vs. frozen.  If your nutrients are too low, feeding pellet/flake food will help increase your PO4 and NO3.  Pellets and flakes are more nutrient dense, and will likely provide more food/waste for your system, which in turn will lead to higher phosphate and nitrate.

One word of caution.  Oftentimes feeding can increase the phosphate (PO4) levels at a much faster rate than nitrate (NO3) levels.  If that is the case, you may need to consider another method for increasing nutrient levels.

5. Manually Remove Dinoflagellates Daily

The most logical way to reduce dinoflagellates is to just suck them out daily.  Using a gravel vac, try to remove as many dinos as you can each day.  Do this when the lights are on, as dinoflagellates are highly photosynthetic and will be most plentiful sometime during your photoperiod.

I would recommend of running your gravel vacuum through a filter sock and into a 5-gallon bucket.  That way, rather than having to perform a water change (thus reducing PO4 and NO3 levels), you can just pour the filter water back into your system. Then just wash the filter sock  and it’s ready to reuse!

A toothbrush can be your best friend in helping your scrape dinos off of live rock or decorations.

You will not win this battle overnight, so don’t be disheartened when you come back the next day and the dinos are back.  Realize that by doing this everyday, you are slowly decreasing their numbers, and will eventually win.

Is this step a huge pain in the butt?  Yes, yes it is!

6. Remove & Replace Filter Sock/Floss/Sponge Every Morning

I know, I know, this is the exact opposite advice I gave about reducing mechanical filtration.  The goal is to keep your NO3 and PO4 elevated. But the goal is also to remove as many dinoflagellates as possible every singe day.  And since dinos tend to release their hold and enter the water column every night, they will be caught in your filter sock/floss/sponge.  Thus it is a good idea to remove them daily.

But since you are changing your sock/floss/sponge daily, you will have to decrease filtration in other ways.  If you have a protein skimmer, put it on a timer and run it for 12 hours a day instead of 24.  Or, if you can adjust your skimmer to produce a more “dry” skim, do that.

And if you don’t use a protein skimmer or any other kind of mechanical filtration, then you’ll either have to feed more or dose PO4 and NO3 directly.

I use both of these wifi outlets below.  They are inexpensive and amazing! You just connect them to your home network, and then you can set up timers to control whatever you want.

7. Stop Use of GFO, Carbon Dosing, & Biopellet Reactors

Here’s the gist:

  • GFO absorbs phosphate, thus removing it from the water column.
  • Carbon dosing helps remove organic matter quickly by increasing the available food source for beneficial bacteria.  This is too aggressive and can reduce your nitrates to zero.
  • Biopellet reactors do the exact same thing as carbon dosing.

So, for the time being, stop using any of these products and let your water get “dirty”.

8. Dose Beneficial Bacteria

Be a little cautious with this one and be sure to test daily.  The goal in adding beneficial bacteria is to have it outcompete dinos for scant resources.  Since both beneficial bacteria and dinoflagellates consume nitrates and phosphates, the goal is to give the good bacteria a leg up.

But be careful here.  Because as you add beneficial bacteria into your tank daily, it will consume more and more of your nutrients.  If you aren’t careful, your nitrates and phosphates may slide back down to zero again, giving the dinos a chance to take over once more.

Not all bacterial supplements are the same.  I recommend using the following:

  • Brightwell Aquatics Microbacter 7 (sold and used here on our site)
  • Dr. Tim’s One & Only
  • Dr. Tim’s Waste Away
  • Underwater Creation’s Vibrant

I wouldn’t dose these all at the same time.  Rather, rotate them.  Day one, use Microbacter 7. Day two, use Waste Away. Day three, you get the idea.

9. Raise The Temperature to 81/82° F

Don’t do this all at once.  Raise it by one degree each day.  Be on the lookout for any stress caused to your fish and corals.  Most should be fine, but some sensitive species or species that are used to much cooler water may become stressed.

I have no idea why this helps, but there are a lot of online feeds, such as this one from Reef Builders, that suggest dinos just don’t do well with higher temperatures.

9. Install UV Sterilizer

This step is not required, but some hobbyists have found a properly installed UV sterilizer to be a game changer. There are so many different species of dinoflagellates, and they all act slightly differently in a saltwater aquarium.

For example, some types of dinoflagellates seem to completely disappear each night, likely releasing into the water column.  This type of dino is perfectly suited to be eradicated with a UV sterilizer. But not all dinflagellates share this characteristic.

If you do end up purchasing a UV sterilizer, be sure to set it up with the proper flow rate. It may also be helpful to disturb the dinoflagellates each night, thus forcing them into the water column, into a filter sock/sponge, and through the UV sterilizer.

Here’s what you’ll need to install a UV sterilizer

  • UV Sterilizer
  • Pump
  • Flexible Tubing
  • Hose Clamps

10. 3-Day Blackout

Since dinoflagellates are highly photosynthetic, a total 3-day blackout can deal them a major setback. I’ve never heard of a 72 hour blackout destroying dinos completely, but it can help you in the battle.

In order for this to work, you need to completely wrap your tank so that almost zero light gets in.  Obviously, you will want to put some sort of air stone inside, and monitor the temperature of the water during this time.

Can you do this even with corals?  Yes, most corals are quite resilient and can easily survive a few days with no light.

What about feeding the fish that are inside. I would recommend doing this at night when the room is completely dark.

Once the three days is over, you absolutely have to keep following this dinoflagellate action plan. Don’t be disheartened when you start to see some dinoflagellates come back after the blackout.  That was always going to happen.  But hopefully you removed enough dinos to give yourself a better chance at eradicating them.

aquarium wrapped completely in cardboard and duct tape

11. Hydrogen Peroxide Dose

I don’t recommend adding hydrogen peroxide to your aquarium, but some aquarists have found it helpful to get rid of dinoflagellates.  If you are at your wits end and have tried everything else, check out this Reef2Reef thread.