The Salty Side: Saltwater Aquariums for Beginners

How To Get Rid of Diatoms

how to get rid of diatoms saltwater aquarium

They may look unsightly and you’re certainly not alone if you’re wondering how to get rid of diatoms in your saltwater aquarium.  

In this article I will give you my tips on how to deal with diatoms, should you wish to speed up the process.

What are diatoms?

Diatoms (Bacillariophyceae) are one of the first algae, or microalgae to be exact, that will emerge when setting up a new saltwater aquarium.  A bloom of diatoms appear as a light film over your new sand, rocks and glass and is brown in colour.  

A diatom bloom is all part of the natural process as your tank matures.

What causes a diatom bloom?

In a reef tank, diatoms appear because there are silicates available for them to feed on.  A diatom’s cell walls are made from this silica which, when looking at them under a microscope, gives them their glassy appearance.

Silicates are introduced mainly by sand (unrinsed or not) and/or tap water which contains silicates.

Once silicates are no longer in your saltwater aquarium, the diatoms will naturally die away.  

get rid of diatoms

How did silicates get into my tank?

Silicates are mainly introduced to your aquarium with new substrate, namely sand.  However, water changes carried out with RO water also has the potential to add silicates to your system. RO/DI water has less potential because it includes a DI resin pod but this depends on your mains supply. I had to have two DI resin pods installed to no longer pick up silicates on a test kit. Ensuring that your top off water, and water used for water changes, has zero silicates will mean that none are being added to your tank.  

New to saltwater tanks? Why not download our very helpful guide to setting up your first tank here.

What do diatoms look like?

The only way to get a true identification of diatoms is to look at them under a microscope.  They are too small to be seen with the naked eye.  Although they appear as a large brown mass, they are in fact microscopic glassy looking cells.

Diatom algae (Bacillariophyta)

How to get rid of diatoms

It is worth noting that diatoms will naturally die off once the silicates in your aquarium have been depleted.  This may take two weeks or perhaps even a month but if you’re patient, it will pass.  

However, if you’re maybe not so patient, you can try some following to get rid of diatoms sooner.  

1. Use powerheads effectively

Angle your powerheads towards the lower part of your tank.  This will create a vertical movement of water which will in turn keep diatoms suspended within the water column.  The diatoms will then find their way through the filtering system and protein skimmer. 

2. Add diatom-eating snails

So, what eats diatoms?  Snails!  Nerite, Cerith and Trochus snails are all known to eat diatoms.  Adding these to your saltwater aquarium will certainly help reduce the population and clear up your tank quicker than if you didn’t.

3. Turning off lighting

Turning the lights off in your tank for a few days will help, especially if used in conjunction with using powerheads to blow the diatoms off the affected surfaces and by adding the snails mentioned above.   

Of course remember that when turning the lights back on, the diatoms will return if silicates are still available for them to feed on.  The advantage is that if doing all these methods in combination, the bloom may not be bad as before and could be less noticeable.

4. Purchasing a protein skimmer

If you don’t already have a protein skimmer, you might want to consider getting one.  Usually they are worth getting if your tank is larger than 25 gallons (100 liters).  A skimmer is something you will not regret buying.    

If you do not have place for one in your sump, there are protein skimmers that you can hang from the side of your aquarium.

Check out my guide on the best protein skimmers for your size aquarium.

What eats diatoms?

If you’re struggling with a diatom algae bloom in your saltwater tank, certain snails are known to eat diatoms.  Among them are nerite, cerith, trochus snails and tiger conch.

what eats diatoms saltwater aquarium

Trochus snail

Dead diatom removal

Once they start dying, diatoms will start disappearing from the rocks, sand and glass.  It may be worth using a turkey baster to blow the remains of the diatoms off surfaces. They will then find their way into your filtration system. 

Remember to clean out your filtration system, such as filter socks, after a large clean up.  This is to reduce a spike in nitrates which can occur with such a die off.

Do diatoms mean my tank is cycled?

The only method of ensuring your tank is fully cycled is to keep note of your ammonia, nitrite and nitrate levels.

Read this article for more help.

Just starting out in the saltwater hobby? Get your copy of How To Set Up A Successful Saltwater Aquarium ebook today.

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

How long does a diatom bloom last?

A diatom bloom usually lasts a few weeks.  Once they have depleted all the silicates in your tank they will naturally die away.  You will notice that their color will start to fade at which point you can start cleaning the rocks and glass and siphoning the sand in order to remove them from your aquarium.

cycle a saltwater tank

Diatoms in an established tank

If you are experiencing diatoms in an established aquarium, one major cause could be the addition of new sand.

Another reason is that your RO/DI system may either be faulty or the DI resin needs to be changed.  

Have you recently changed your lighting?  This can often cause a diatom bloom as they require light to photosynthesize.

How to prevent or minimise a diatom bloom

As we know the main causes of a diatom bloom in a reef tank, it makes it easier to know how to prevent, or at least minimise, a bloom when it occurs. 

The following tips will help:

1. Always rinse new sand

As you probably know by now, the main way in which diatoms bloom in a saltwater aquarium is through the addition of sand.   Unrinsed sand in particular.  Silicates are abundant in substrate and diatoms need silicates in order to survive.

Even in established tanks, if you are thinking of adding new sand, ensure that you rinse it well with RO/DI water.  

2. Never use tap water for you saltwater aquarium

Ensure that you are using RO/DI water and not tap water when adding water to your tank.  Tap water commonly contains silicates and by using it, you are only feeding the diatoms, therefore extending their stay. 

This also applies to mixed salt water.  If you are not mixing your own salt water then you will need to ensure that the water used before mixing, is silicate free, ie. RO/DI water.

3. Change DI resin regularly

TDS meters are often sold in conjunction with RO/DI units, however a TDS meter only measures Total Dissolved Solids of which silicates is not one. Therefore if your TDS meter is measuring 0 then this does not mean you have no silicates. Only a silicate test kit can pick up silicates in the water.

DI resin does however aid in removing silicates from the main water. If you should pick up silicates on a test kit its time to replace the DI resin (or add more).

Can diatoms outcompete dinoflagellates?

Dinoflagellates are by far the worst algae a saltwater aquarium can suffer from. I personally had them for over a year until I began purposely dosing my tank with a chemical called water glass. Water glass is Sodium Silicate. By adding silicate to my tank on a daily basis the diatoms were able to outcompete the dinoflagellates. 


So as you can see from the above, a diatom bloom should disappear once all silicates have been depleted.  Although it will minimise them in the short term, no amount of cleaning will completely rid your saltwater aquarium of diatoms if there are still silicates in the water. 


Hi, my name is Craig.
I am the owner of The Salty Side.
Firstly, thank you for visiting us. If you have found this article to be informative, and you now have a better understanding of the topic, then my job is done.

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