The Salty Side: Saltwater Aquariums for Beginners

How To Get Rid Of Dinoflagellates In a Saltwater Tank

In all my years of keeping a marine tank I had never had to deal with Dinoflagellates … until recently.  It reared it’s ugly head in my new 5ft tank and I imagined the worse possible scenario, having read multiple accounts of dire situations.

Joining Dinoflagellate groups and forums did nothing to abate my fears. In fact they did quite the opposite. I was flooded with a multitude of methods to eradicate, all of which seemed to have inconsistent results.  If you learn nothing else in marine keeping, learn just one thing, do your own research!

My hope is that by reading through this article you will gain some insight from my experience with this terrible algae, and it will help you to get rid of dinoflagellates in a saltwater tank.

How to identify dino in a marine tank?

Generally speaking, dinoflagellates can be identified by their brown mat-like appearance with trapped bubbles just beneath the surface.  As it matures, the mat has the potential to spread rapidly and over everything.

The surface bubbles begin to push upwards and this creates sweeping tendrils that reach into the water column.  Dinoflagellate consistency is often described as snotty. It is very easy to siphon up, but within a matter of hours can appear in the same place again.

Is dino always 'snotty' in appearance?

Dinoflagellates do not always take on the typical snotty appearance, which I discovered while I was battling to kill it.  It can also take the form of simple brown film algae that mats together. The overall look of your tank will be brown, including brown film on the glass. It is easy to remove with a siphon, but just as quick to reappear once more.

For beginners to marine keeping, diatom and even cyanobacteria can be confused with dinoflagellates. The most conclusive way in which to ensure you do not have dino is to look under a microscope.

dinoflagellates or dino
Dino confirmed with a microscope - no bubbles and not snotty

Why do I have dinoflagellates in my new tank?

This is an easy answer!  Your nitrate and phosphate levels in your saltwater aquarium have hit zero.  Unfortunately, this is very easy to achieve with a new tank setup. I have been in marine for many years and managed to hit zero too.

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This ebook hopes to guide you past the mistakes I have made over the years.

What do dinoflagellates look like under a microscope?

Dino individuals come in a number of variations but are all unicellular and typically the oval-ish in shape. Some are completely oval, while others are more teardrop shaped.  Some, like Ostreopsis sp., move in a tethered like motion, as if they are attached to a central point.  Others follow random patterns.

In just one water droplet extracted from your infected rockwork with a syringe, 
looking through a microscope, you will see thousands of dinoflagellates.   

Where can dino be found in a saltwater tank?

Dinoflagellates can cover every surface in direct line with your lighting.  Depending on the type they can blanket your rockwork, your sand, your powerheads and wavemakers and every other surface where it can gain a purchase. 

Understanding dinoflagellates

Before I go into methods I tried to eliminate dinoflagellates, it’s important to know what you are dealing with, and consequently how these methods came to be.  Equally so, it is important to understand why one method will work for one tank and not for another.

As a seasoned reef keeper, even I fell into the trap of trying every method out there without stopping to understand what I was dealing with!  
When I stopped, and had them identified with a microscope, and spoke to people who really knew what they were talking about, then things started to take a turn for the better.

In my case, I found out I was dealing with Amphidinium & Ostreopsis dinoflagellates. Amphidinium is substrate and rock dwelling dinoflagellate that does not often enter the water column.  Ostreopsis does enter the water column every night and spreads rapidly over everything.

So now I knew I had two, not one, but TWO types to deal with!!


Dinoflagellates are possibly one of the hardest algae to get control of and eliminate. Even with the following control methods in place, do not expect it to disappear overnight. For most hobbyists, the emergence of dinoflagellates can mean months of ongoing treatment, unless you are lucky.

STEP 1. Raise your nutrient levels

Your very first step in the fight against dino is to immediately ensure that your nitrate and phosphate levels are above zero. Very often dino emerges in new setups because nutrient levels have bottomed out. If you have tested your nitrate and phosphate levels and found one or both of them at zero, you will need to get them up again.

Raising phosphate:

When I experienced dinoflagellates, I could not get my phosphate to register on my Hanna test kit.  I knew that my nitrate had bottomed out too, but they were now above zero. I knew I needed to increase my phosphate so took the decision to dose phosphate using Brightwell Aquatics NeoPhos. Importantly, do not raise your phosphate above 0.03ppm.  Any higher than 0.03ppm will encourage green hair algae, creating another problem that you may have to deal with – and I’m unfortunately speaking from experience. 

For more information on Green Hair Algae, read this article

You also have the option of using a cheaper method of dosing phosphate. I have used both successfully. Click here to find instructions on dosing with Tri-Sodium Phosphate.

Raising nitrate:

My nitrate was already sitting at 20ppm, not great, but better than zero. I was happy to leave it there.  However, if your nitrate is hitting zero it needs to be increased to at least 5ppm and no more. You can do this safely using Brightwell Aquatics NeoNitro.

Again, if you are looking for a cheaper option to dose nitrate, click here to find instructions on dosing with Potassium Nitrate. I have also used this successfully.

Raising your nutrient levels is absolutely critical. Use the links provided above for products that will achieve this for you. Aim to have your phosphate level sitting between 0.01ppm and 0.03ppm.  Aim to have your nitrate level sitting between 2ppm and 5ppm and no higher.  Having higher values of either phosphate or nitrate can lead to a breakout of green hair algae unless you have a coral dense system.

STEP 2. Get the dinoflagellates identified

For identification you are going to have to get your hands on a microscope because only once you find out which particular dino you have, can you act decisively.  

By purchasing a microscope like this one, I was able to take photos and videos of the particular dino infesting my tank. Then you head over to this Facebook page for the best help you will find. Upload your photos and videos, and get invaluable help in your fight against dinoflagellates.

AmScope M150C-I 40X-1000X All-Metal Optical Glass Lenses Cordless LED Student Biological Compound Microscope, Silver, White, Black
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STEP 3. Raise the oxygen level in your tank

Dino utilise carbon dioxide as a food source, so if possible we need to limit the available carbon dioxide in your tank.  This is the reason you will often read that reefers claim raising the PH level to 8.3 or above will help in the fight against Dino. pH is directly affected by the available oxygen in your tank. 

Opening a window raises the pH. However, to have any affect against dinoflagellates you need to do a little more than opening a window.  For those of us living in colder climates, the thought of opening a window isn’t a great one. Increasing oxygen alone will not get rid of dinoflagellates in a saltwater aquarium, but it does help in fighting back, by improving the overall wellbeing of your tank.

Below are a few methods we can use to raise the oxygen level in our tanks, with hydrogen peroxide being the preferred method.

Start dosing hydrogen peroxide in a saltwater aquarium:

Start dosing 3% hydrogen peroxide at a rate of 1ml per 3 gallons daily. Do this as the lights go out as this is the time that free swimming dinoflagellates enter the water column.  

Peroxide temporarily raises the oxygen and has the potential to disrupt the life cycle of dino. Some reefers are uneasy about using peroxide, and I’ll admit I was one of those until I started using it too. Hydrogen peroxide oxidates the moment it hits water and raises the level of oxygen in your tank for about 4 hours. 

Micro-bubbling a saltwater tank:

There are forums that suggest ‘micro bubbling’ by placing an air pump outside your property and running an airline to a limestone diffuser in your sump. 

This certainly does increase oxygen but depending on where your tank is located in your house it might not be possible.  It is also worth knowing that this method has the potential to cause salt creep over a longer period of time.

Increase oxygen through your skimmer:

Connect your skimmer up to tubing that you run to the outside of your house. Again, this would certainly work but you may have the same limitations as above. You may not be able to run a tube to outside.

Install a PIV unit in your property:

Installing a PIV unit in your property will displace the carbon dioxide accumulated indoors with more oxygen from fresh air outside. 

Most modern properties are so well sealed that they can become oxygen deficient especially over the colder months. This means that your tank could be oxygen deficient too.  The primary reason PIV units are installed is to prevent condensation and stale air in corners.

Add a Sochting Oxydator to your system:

A Sochting Oxydator is an inexpensive addition to a system and for me I believe it was worth the expense as a tool to help elevate the pH.

You can read more about it

STEP 4. Dosing phytoplankton and adding copepods

Phytoplankton is an essential part of the food chain in the ocean and the reefs of the world. It is also extremely beneficial in a saltwater aquarium. It feeds copepods and amphipods. These pods in turn consume organic waste, bacteria, detritus and add to the diversity in a reef tank. This means that they lend a helping hand getting rid of dinoflagellates too. Phytoplankton therefore, indirectly helps to keep your aquarium alive with pods that help in the battle against dinoflagellates.     

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Adding phytoplankton and pods cannot be underestimated. The addition of copepods, and amphipods if you can find them, will help your system tremendously. They may be that small that you will find it difficult to understand the impact they can have in helping to keep your system clean and the diversity they bring (they are after all the forgotten members of your system’s clean up crew), but they also feed on dino. Combine pods with phytoplankton and you will have a pod explosion.

STEP 5. Decrease lighting and reduce schedule

Dinoflagellates are photosynthetic, which means that they rely on light energy for food. You will notice how they diminish overnight and return in abundance during the day. Turn your lights down, and reduce peak lighting to 6 hours only. By doing this you are disabling the dinoflagellates in one more way.  I had my lights set at 10% white and 60% blue for the duration of the treatment.

STEP 6. Purchase a 5 micron filter sock

As part of practicing manual removal, place a 5 micron filter sock in your sump and siphon all visible dinoflagellate masses into the sock. The sock will catch the dino but allow the water to pass through it.
If you do not have a sump then siphon through the sock into a bucket and return the water from your bucket back into your system.

STEP 7. Siphon you sand bed

If you find out that you have substrate dwelling dino, such as Amphidinium, and you’ll probably have noticed them on your sand already, its time to siphon your sand bed.

It’s not something that I would normally have done, but it did work in solving my issue. You need to ensure that every inch of your sand bed is siphoned clean to remove as many of them as possible. This needs to be done at least three weeks in a row.

I ended up doing a 20% water change which each siphon.

STEP 8. Water Glass: Time to out-compete the dinoflagellates

Whether your dino are identified as Ostreopsis, Amphidinium or Cooila, they all flourish in a tank without competition. They have the upper hand.
This is where things really took a turn for the good with my tank – when I began dosing Water Glass (Sodium Silicate). I had tried everything and didn’t expect much, but I have been surprised.

By dosing Water Glass, you are adding controlled amounts of silicates into your system daily and encouraging a diatom bloom. It sounds worse than it is. I have not seen a diatom bloom at all, but the dinoflagellates decreased everyday as they were outcompeted by the diatom.

The aim is to slowly increase the daily dosage until you hit 3ppm, and then maintain the dose there until the dino start to disappear.
Dosage guidance: 3ppm = 3ml/560L  
Your starting dose should start low. To give you an idea, my tank volume is 560L (coincidence) and I started at 0.5ml the first night, and increased by 0.2ml every night until I reached 3ml goal.

Water Glass can be found on Ebay. You should be looking for a 36% – 41% solution.

STEP 9. Adding a UV Sterilizer

A UV Sterilizer will not work with some dino, but does work with others.  If you find that you have Ostreopsis then a UV is the quickest way to deal with them.

Please be aware that not any old sterilizer will work. In order for it to be affective it should be run at 1W per 3 gallons (12 liters). If you have a 300L tank you need a 25W UV sterilizer. My water volume is 560L and I run a 55W UV which is more than required, but it has worked.

The flow rate through the sterilizer, for it to kill any free swimming dinoflagellates that pass through it, should be between 65 to 100gph (350 to 550lph).

In the first two weeks, place the UV pump directly in the display. Have it feed through the UV and back into the display. If you direct it into the sump, you may have to adjust your return pump to compensate.

STEP 10. Finally...

Don’t stop dosing trace elements. An informative poll on Mack’s Reef has found that a deficiency in certain trace elements help dinoflagellates proliferate. So keep those trace elements going in. 

The Total Blackout

While you are correcting your nitrate and phosphate levels, and increasing the oxygen being introduced into your tank, you could try a total blackout.

It is worth saying that this is a 50/50 thing. It works for some and not for others. It did not for me, but that does not mean it won’t work for you.

A total blackout does not mean turning the lights off only.  You need to ensure there will be absolutely no light getting into your tank, and the easiest and most practical way of achieving this is by using kitchen aluminum foil.

Don’t be tempted into using black trash bags. If you hold these up to the light you will see pin pricks of light coming through. You want absolutely no light coming through.

The blackout period should be 3 – 5 days, preferably 5 days to ensure you have allowed maximum time to hopefully won the battle, but not at the detriment of your corals and fish.  

When you remove the foil your tank will look amazing, but the telling part will be if no bubbles begin to appear on surfaces after 10-12 days.  Hopefully you may be one of the lucky ones and you’ll have gotten rid of the dinoflagellates in your aquarium.

Unfortunately, this method did not work for me.

What experience and hindsight has taught me about dinoflagellates.

I have used every method suggested online to get rid of dino, but nothing completed the job.  I have used Fauna Marin Dino X as a standalone treatment as well as Hydrogen Peroxide, Vibrant, the dirty method, no water changes for 8 months, the starvation method and even dosing yeast of all things!

In hindsight, all the above treatments culminated in my system becoming less and less stable. The dino was diminished but still there.  Then the worst happened … my fish came down with Marine Velvet.  A year of the worst ‘algae’ a marine tank can have was topped off by the worst fish disease a marine tank can have! I learned the hard way.  I will ALWAYS quarantine new fish and invertebrates and will continue to advise anyone else to do the same.  You can see my setup here.

To cure Marine Velvet in a saltwater tank is to go fallow. To go fallow is to keep your tank fishless. In the case of velvet this is a minimum period of 6 weeks. I did 10 weeks. With no fish or coral in the tank I turned the lights off for 7 of the 10 weeks.  Without fish in the tank my pod population absolutely exploded. I could look at the rockwork 4 weeks in and they were crawling with amphipods and copepods.

I had decided to turn the lights back on at the end of the 7 week period to ascertain my next step in dinoflagellate control. If they came back I had three weeks to shut the tank down, and re-boot with new rock, sand and water.  I held my breath for 14 days, expecting them to reappear at this stage. They came back … after 7 weeks with no lights on.

There's a lot to be said for live rock

Unfortunately, dinoflagellates are tenacious in the extreme. The good news is you will beat them.  I have cycled five tanks in my time as a reefer. Three of those tanks were cycled with live rock and none of which experienced dinoflagellates.

My very first tank some twenty years ago, was cycled with dry rock. At the time there was no such thing as bacteria in a bottle and quick cycling methods. You just had to be patient and wait out the 6 to 8 week cycle which was brought on by a simple decaying prawn which you had added as an ammonia source. The lights stayed off and nothing interesting happened.

The following three tanks were cycled using Fiji live rock (which is no longer available) and ATM Colony. I believe the life, the micro fauna and flora, living on the live rock gave dinoflagellates no opportunity to gain a foothold.

This leads us to my current tank.  I started it with dry Marco rock and ATM Colony.  As this was an upgrade, I transferred my fish immediately from the smaller tank and all was well until a week later.  With no life on the dry rock, dinoflagellates took full occupancy, and advantage.

Experience counts for a lot in this hobby, and having battled some of the worst it can throw at me, I have written an ebook that I hope will help new aquarists side step some of the difficulties I have experienced.

The takeaway from this is that next time, I will only use live rock

Other methods I tried but failed...

The Dirty Method

The aim of the dirty method is to allow your nitrate and phosphate to increase to such a point that it will encourage the growth of other algae such as green hair algae, or even cyanobacteria.  These algae will outcompete the dinoflagellates by accommodating all available space on your rockwork, and in fact, any surface where algae/dinoflagellates can grow.

The drawback of course, is if it does work, you are then left with unwanted algae that you then need to get rid of.  This may work for some people, but it did not work for me.

The Black Out Method

Yes, I did a few of these black outs, and of all the methods, this was the least successful.
Dinoflagellates are known to be photosynthetic. This means that they need light to survive, and in the absence of light they will die.  

HOWEVER, not all varieties of dinoflagellates are reliant on a light source to survive.

The Starvation Method

The starvation method refers to removing all possible forms of sustenance available to the Dinoflagellates. 

This method requires the following:

DO NOT carry out any water changes. Water changes reintroduce trace elements which can be utilised by the Dino.
Maintain LOW nutrients. This acts to starve the Dino of nitrate and phosphate (however it is also well known that Dinoflagellates require very little nitrate and phosphate to survive)
Discontinue DOSING. Do not dose trace elements and amino acids which can be utilised by the Dino.
DO NOT disturb the Dino. It is thought that this could cause them to spread.
Raise KH. Increase your alkalinity to 8.3dkh or above.
Wait it out. Be prepared for months!

Again, this did not work for me.


I Tried Vibrant For Control Of Dinoflagellates

I began by following the instructions, which is 1ml per 10 Gallons of water. 
They recommend dosing clean tanks every two weeks, and dosing dirty tanks once a week.

I began dosing once a week. My tank volume required that I dose 15ml per application. 

I noticed the day after the first dose that there was no continued growth of the Dino. However, the following day it was growing slowly again, sending snotty tendrils into the water column.
I left it and dosed again after a week.

Again, after the second dose, I noticed no discernible growth or spread on the day after dosing.

I took the plunge and dosed again the very next day.
There was no growth again the following day. 

From that day on I dosed 15ml per day, and watched as the Dino stopped growing and then started noticeably reducing day by day.


I was still getting blown film algae (due to high nitrate), and the remainder of the hair algae was there, slowly being eaten by my resident population of Mexican snails, but the Dino was definitely in retreat.

I was also cleaning off the rock work with the turkey baster on the weekends to properly monitor the progress. Three weeks in and I had only a handful of Dino bubbles trying to hang on.

After five weeks I thought I was dino free, until I looked under the microscope.

So there you have it...

I just hope this article has helped someone who was in the same predicament I was in. I’ve crammed it full of everything that I have found to be relevant and that has worked for me.

Good luck!

I suffered with dinoflagellates for more than a year and I can now say that my system has recovered from the hell it has been through. I am dino free! If I knew then what I know now I would have done things completely differently and I’m sure I would have been free of dinoflagellates much sooner. 

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