How To Get Rid Of Diatoms (Brown Algae)

Image Credit kiwis via Reef2Reef
Image Credit kiwis via Reef2Reef

How To Get Rid Of Diatoms (Brown Algae)


There is nothing worse for aquarists than an unwelcomed guest in our reef aquariums. Brown algae are just one of the many guests that weren’t invited to our aquariums but somehow managed to find their way in anyway and now they won’t leave. However, there is no reason to worry because we are going to discuss what these brown algae want from your tank and how to kick them out once and for all.

What are Diatoms or brown algae?

Diatoms are relatively tame for algae that is very common in aquariums.  They are considered microalgae and can cover your tank in tiny brown particles. It usually will appear like your fish have been letting their home rust over but lime away won’t help in this situation. This species of algae thrive on the nitrates, phosphates, and silicates in your aquarium.

How To Identify Brown Algae?

The easiest way to identity Diatom algae is by their color. If your rocks, substrate, and coral are being covered in a brown film, it is most likely the Diatoms that are spreading. If you are willing to get your hands a little dirty, you can reach into your tank and run a finger over a brown covered surface. If the film that comes off feels gritty, the brown film is most likely Diatoms. 

What causes Diatom bloom?

The most common time for Diatom algae bloom is when you are setting up a new tank system. During its initial cycling, the tank has an imbalance of compounds like nitrite and ammonia which is what the Diatom algae feed off of. 

However, that also means that if your tank ever has an imbalance in its nitrogen cycle, you very likely will see Diatoms begin to set up camp in your tank. 

How long does a Diatom bloom last?

Diatom algae bloom can last forever technically, which is why we try to target the source of their persistence. If you can target their food supply, Diatom algae will begin to disappear fairly quickly but the tricky part is eradicating enough phosphates and nitrates for long enough where the brown algae will completely be removed from your tank’s system. 

Why do I keep getting Diatom Algae?

If your tank is fully matured and you have been removing your brown algae fairly regularly then that should be a red flag that there is something wrong. You want to review the list below of possible issues that might be causing the imbalance in your tank.

  • Too many fish in your aquarium
  • Overfeeding your fish
  • Are you performing regular water changes?
  • Not enough lighting
  • Copper additives (medications and other treatments)
  • What is your water quality? Are there Nitrates or silicates?
  • Is your equipment working properly, especially your filter?
  • Is your water properly treated before you add it to your tank?

Why get rid of Diatoms?

Diatom algae are not necessarily villains in this scenario. They don’t cause harm to your tank but can be unsightly and can give your tank a “dirty” look. Plus, they are often an indication that something is wrong with your water quality so it is best to remove them and deal with the source of the problem.

What does a Diatom algae eat?

Diatoms eat the silicates that can come in the new substrate or even in salt mixes that you use to mix that your use for your saltwater. Nitrate is also a favorite of Diatoms so if your tank is creating more nitrate than it knows what to do with there is a risk for a Diatom bloom. 

Can brown algae kill my fish?

Nope! You have nothing to worry about. Diatom algae can not kill fish themselves however they can hurt the plants in your aquarium. 

Diatoms are a sign that something in your tank is off though. The ripple effect of which means that your fish might be in jeopardy depending on the imbalance. It is best to figure out the source quickly so you can deal with the issue. Diatom algae act as a great initial warning sign that something isn’t quite right in your reef tank.

How to get rid of Diatoms

If you are still cycling your tank, in all likelihood, the brown algae will simply die off before you add your fish and corals. There is no reason that you should work to remove something that will simply remove itself in due time. However, if you have a mature tank and are experiencing Diatom bloom then you do a few things first. The initial priority is identifying what might have caused the Diatom bloom in the first place. Check the water quality and your equipment to ensure that everything is up to snuff. 

  • Perform water changes in your tank with quality water. You may have become a little lax in your water-changing routine or maybe the water that you have been using hasn’t been properly treated before you create your saltwater. Use water that has been treated with a RODI unit to ensure that it is ready for mixing. Perform water changes once a week for about 25 percent of the water.
  • Remove algae from your tank glass. You will need an algae scraper. I would try to get one that is magnetic or has a long handle so you can reach those hard-to-reach spaces. Scrub the sides of your tank and remove the scrubber so you can remove some of the build-ups of brown algae that will be accumulating there. If available use a small tub of clean water to help remove some of the build-ups from the scrapper.  The main thing you want to do while performing this task is to make sure you are picking up all the brown algae that you run over with the scraper. You don’t want to push some of the algae off the glass just for it to find a new home somewhere else in your tank. We are trying to remove the Diatom algae from the aquariums not mix them around inside the tank. A great way to keep more algae on the scraper and less in the water column is to scrub from bottom to top. Drag the scraper towards the surface and remove it carefully before the scraper is just pushing the algae around.
  • Remove algae from your substrate. The process will depend on the type of substrate you have but we will cover a couple of examples. Gravel is probably the easiest to remove the Diatoms from. You only need to use a gravel vacuum to clear up the algae. Be careful not to bury the Diatoms, we are trying to suck it up not store it away to haunt us later. Sand is not nearly as easy. Keep your vacuum above the sand to suck up any surface-level waste and then reduce the suction by pinching the tube. The rest of the process requires that you carefully mix up the sand with the suction tube and then bring it to the surface without pinching it. This way you slowly reveal more waste on the surface and can safely vacuum it up without sucking up all your substrate. 
  • Remove any decor that is removable to easily remove brown algae on those surfaces. Since these pieces are removed you can really make sure they are cleaned before reintroducing them to your display tank. You can use a scraper as we have or a burhs to remove the algae. If you are not able to remove the algae from your decor consider using chemicals to remove the algae from the object. Remember to thoroughly rinse the object so there isn’t any leftover chemical on it when you try to put it back in the tank. 
  • Increase the flow of water if you are able but this only works if there are no creatures in your tank that don’t respond well to high flow. If you can’t necessarily increase flow, you should make sure that there are no dead zones in your tank. Dead zones are a breeding ground for algae so eliminating them will help in the long run. If you can increase the flow, you are effectively preventing the algae from being able to attach themselves to certain surfaces in your tank. 
  • You can try to use a UV sterilizer which will use UV rays to attack the DNA of the algae. It doesn’t kill the algae but it eliminates its ability to reproduce which makes clearing them out a little easier. The UV sterilizer is also very good for general tank maintenance and extra support to ward off disease and other algae pests.

Will Vibrant kill Diatoms?

Vibrant does a pretty good job clearing up the water in your aquarium of any algae that may be present. Vibrant introduced bacteria that go after algae in different ways like attacking its food source. Vibrant won’t clear up your aquarium in a week but it will help to keep not only Diatoms but other types of algae at a minimum. 

Follow the manufacturer’s instructions on the bottle. Depending on the size of your tank and the problem you are trying to address the specific dosage may change. You should aim for one dose a week unless it appears that the algae are being resilient, if that is the case consider upping the rate to two doses a week. 

You don’t want to add too much Vibrant too quickly because even though it is depleting your algae problem quickly, your tank is not prepared for the amount of waste that it will need to process. Take it slow and steady to ensure the problem goes away without any additional issues arising. 

Will Phosguard remove Diatoms?

Seachem Phosguard is designed to remove phosphate and silicates from the water supply which are two of Diatom’s favorite foods. Diatoms will quickly die off when their food source isn’t sufficient enough to sustain them. 

You want to ensure that the product is being distributed throughout your tank. Using your sump (at a high flow)  as the distributor might be a good start to the process or place it in your canister filters. Within a few days, you should begin to see some difference in the total amount of Diatoms in your tank. 

How to prevent Diatoms from growing?

The best offense will always be a good defense. You should try to implement some of these care practices into your own routine to help prevent future Diatom blooms in your fish tank. Nothing is ever 100 percent secure because failures and other unforeseen circumstances occur but we can try our best. 

  • Introduce some sponges into your aquarium as they will help to reduce the level of silicate in your water supply if you are having trouble removing them completely yourself. 
  • Don’t overfeed your fish! All the leftover food that your fish are not able to eat will slowly turn into large amounts of nitrate and phosphate which is the exact food source Diatoms need to thrive. You are trying to feed your fish not the pesky algae. 
  • Your water and substrate can be huge carriers of silicates if you aren’t careful. Be sure to use water that has been treated properly and isn’t straight from the tap. If you need help making your tap water safe for your aquarium, check out our article on the topic of making tap water safe for your aquarium.
  • Upgrade your filtration methods to help bring down the levels of nitrate, nitrites, and phosphates from your water. A good protein skimmer will go a long way in reducing the waste buildup in your aquarium.
  • Do your water changes regularly. This is one of the easiest measures you can do to ensure that your aquarium is staying clean. You only need to do 20 percent weekly as long as your saltwater tank is not experiencing any issues. If you notice that your aquarium is having a buildup of waste or algae then increase the percentage of the water that you are changing out. 

Final thoughts

Now you stand a fighting chance against persistent brown algae in your reef aquarium. Though it might be easy to say that you only need to remove the silicates and nitrates from the water to starve the Diatoms, the tricky part is targeting those compounds in the water. If you can successfully reduce their food source, brown algae should be no problem in no time. keep your glass clean and the water changes coming and you will be Diatom free eventually but persistence is key.

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