Nitrate Management in Your Saltwater Aquarium

When setting up new aquariums, most people worry about and focus on ammonia and nitrites.
Everyone knows that cycling a tank with fish is dangerous because of these two compounds, as they
burn the gills and body of the fish as the tank matures. But, once these get to zero, most people are
satisfied and go on adding fish and corals. But, many fail to control the end product of the nitrogen cycle
— nitrates. Because this is not nearly as harmful to inhabitants as ammonia and nitrite, nitrate is often
forgot about until it is too late, and you have already have a problem such as an algae bloom. Even well
established tanks can have these effects pop up. Understanding how to properly control nitrate is a
necessity in this hobby. Thankfully, there are many methods of control. From aquarium substrate to
macro algae to carbon dosing to biological blocks, this article will help you decide which is best for your
set up.

Macro algae as a natural consumer

This is the most common way to control nitrates. Most beginners do a basic search online and set up a
simple refugium with chaetomorpha macro algae and call it a day as far as nitrate control goes. While
this may work for some, I have personally found many other more productive algae species that have
been easier to care for. Chaeto prefers to tumble, so extra powerheads are often used to encourage
this. You can just plop it into the refugium, but it will likely not grow nearly as quickly as it can and
therefore not consume nitrates as well as it is actually able to. But, it is important to note that
chaetomorpha is the least likely to undergo sexual reproduction out of the most popular algae species,
so many people prefer it solely for this reason.

Macro algae such as sea lettuce, Gracilaria species, dragon’s tongue, and Cualerpa species are other
good options. Personally, I prefer Pom Pom Gracilaria as it is a beautiful red color and my tangs enjoy
eating my clippings. No matter what algae you choose to use, make sure you have a good 6,500 K light
or specialized “refugium light” over it. Without a decent light, algae won’t grow and will slowly melt and
die, only adding nutrients back to the tank. Macro must also be trimmed, nutrients are physically
removed from the tank when you do this. If your tank is large enough for tangs, angels, or other algae
eaters, offer them your extra macro as it is usually an appreciated treat! Otherwise, most local aquarium
stores will offer you a little store credit for your trimmings.

Using a deep sand bed

This is an older method, and is tried-and-true. Simply put, you add sand aquarium substrate to a
chamber of your sump until it is about six inches deep and then never touch it again. It created an
anaerobic area where anaerobic bacteria can colonize. This is the bacteria that actually “consumes”
nitrate. Allowing it to flourish in a deep sand bed allows your tank to naturally remove all products of
the nitrogen cycle and turn it back into atmospheric nitrogen.

Although this is a great and efficient method of nitrate control, it comes with a caution. If you disturb an
established deep sand bed, it is very possible to kill tank inhabitants. These anaerobic areas have the
ability to collect toxins, such as hydrogen sulfide. This can happen in shallow sand beds as well if not
stirred regularly, as buried organics often produce this as a waste product. If you are concerned, run
granular ferric oxide (GFO) as it converts this compound to only sulfur (which isn’t toxic), and activated
carbon (which binds the hydrogen sulfide). If you don’t disturb the sand bed, this is a great method of
nitrate control.

Organic carbon dosing

Vodka, sugar, vinegar, and commercial preparations are all ways to dose organic carbon into your tank.
This new source of carbon in the tank encourages the growth of denitrifying bacteria that cannot survive
or reproduce in tanks with normal levels of carbon. These bacteria are then removed via protein
skimming. If dosed correctly, this effectively reduces or may even eliminate nitrates (and phosphates)
from your system. Be sure to increase oxygenation in the tank while using this method as the new
bacteria uses up a lot of the available oxygen.

When using this method, keep in mind that you must dose daily, and skipping a day can cause nutrient
levels to explode once again and potentially harm corals and invertebrates. Many aquarists also
experience diatom and cyanobacteria blooms while using organic carbon as it may cause an inbalance
between nitrate and phosphate levels. This is also common when days are skipped or tanks are taken off
of carbon dosing all together. I have personally experienced floating brown slime algae, it was quite
unsightly. Because of the constant need for carbon dosing and the side effects from simply missing a day
or “detoxing” from the carbon source, this is my least preferred method of nutrient control. Although,
many “biopellet” products that are placed into reactors are available now, and I do like this method as it
is a constant supply of carbon that is easy to maintain.

Biological media blocks

Much like using aquarium substrate to create a deep sand bed, biological media blocks aim to provide
anaerobic bacteria a place to colonize. These media are so porous that near the center, there are areas
where no oxygen can permeate. Due to how much bacteria (aerobic and anaerobic) this media can
house, it can also be used instead of live rock for those who want a minimalist look in their tank. To
truly have anaerobic areas, get the largest block offered (I typically recommend at least a four by four by
four inch cube, preferably larger (such as eight by eight by four inch blocks). Some newer media has
been released recently that claim their small pelleted media has anaerobic areas, but I am extremely
skeptical and have not done proper testing with these. Marine Pure blocks are what I typically
recommend. Keep in mind that these blocks are not an immediate nitrate reducer, they take around
three months to colonize before you will see much of a difference.

Closing thoughts

Even though many people don’t think about nitrate control when first setting up their tank, it is an
essential part of the nitrification cycle that needs to be present in your aquarium in order to keep it as
healthy as possible and an environment in which your fish, coral, and invertebrates can thrive. If you
don’t keep nitrates under control, algae blooms and cyanobacteria are inevitable and can quickly turn a
beautiful tank into an unsightly mess. Even large water changes are often unable to keep up with the
amount of biological waste a large reef tank produces, so it is important to ensure that your tank can
naturally handle that bioload without becoming overwhelmed. Whether you rely on organic carbon,
macro algae, media blocks, deep aquarium substrate, or another method I haven’t covered, make sure
you address nitrate control within your system so your tank can thrive for years to come!

84 thoughts on “Nitrate Management in Your Saltwater Aquarium”

  1. I used microalgae as my main source of nitrate control. I learn that cheato won’t thrive if nutrients are low. Deep sand beds has its pro and cons. Deep sand beds has cause majo problems for me if it’s not clean or stirred often

  2. Mark Strachan

    Having a proper load of good rock in the tank is also essential. Not all rock is created equal. Rock such as pukani is highly pourus and great for harboring anearobic bacteria for nutrient control whereas base rock has almost none. A properly landscaped tank will naturally take care if itself

  3. conner stumpf

    Even without a fuge of any sort I’ve had difficulties keeping detectable nitrates. Have gone into the dosing method to keep them detectable

  4. I’ve had saltwater tanks for more than 30 years – fish only. I’ve done more water changes than I care to admit. . . so starting a reef tank was not something I ever though possible without weekly water changes.

    I started my first reef tank about six months ago after learning about the Triton method. I am happy to say that while the reef building process is still ongoing as I grow my tank inhabitants, I could not be happier with the results. My refugium: Chaeto refugium starter pack that includes the ceramic blocks,in first chamber lit up with a Kessil H380 six hours per night, a protein skimmer in second section with the heater and a bag of carbon, and a return pump that generates 10x turnover. My tank has zero ammonia, zero nitrite, and near zero nitrate with ZERO water changes after six months. Fish and inverts are healthy and the corals are growing. Building the natural ecosystem takes time but it is worth it.

  5. brennan lottes

    I have a refugium and a dsb to control nitrates. The refugium binds up the nitrates so I can just scoop them out of the tank as a ball of algae

  6. John L Fenstermaker

    Deep sand beds have always worked for me. Macro algae works well too in a sump. My Tang makes short work of any that ‘escapes’.

  7. Martin Chartier

    Great article. I’m a civil engineer that has designed wastewater treatment plants, requiring tertiary treatment. I look forward to designing and/or setting up a display refugium with macro algae and biological media blocks.

  8. I have tried chaeto and Mangrove plants for my refugium and the mangroves really thrive and grow but the chaeto only lasted a short time.
    So I would really recommend mangrove plants over chaeto even though mangroves are more expensive!

  9. YOU MUST FOLLOW THESE METHODS! USE ALGAE BARN PRODUCTS TO ESTABLISH YOUR TANK. I LOST THOUSANDS OF DOLLARS OF FISH AND CORALS BY RUSHING IT AND NOT SETTING UP THE REFUGIUM AND TANK WITH THEIR ALGAE AND PODS. A MUST!

  10. Love this place orders always show up on time and alive. This is the Only place I trust for algae never buy from lfs or get from friend can contain fish disease. Unless your gonna qt it. I run my fuge with a phosphate reactor no carbon and only run my skimmer half the amount of time don’t leave on all the time makes my nitrates to stay below 5 if ran all time it would be zero. I like a little for coral growth in my reef tank. And yes you can have very successful tanks with a tiny bit of nitrates.

  11. I have a nano tank with both media blocks and micro algae, but still have problems with this. I know that I am a classic over feeder, but this is always my ONLY high level when testing.

  12. I’m a firm believer in natural foods and filtration over processed foods and chemicals. Nice to have a one stop shop that feels the same way.

  13. Thanks for the informative article. I didn’t realize that carbon dosing and vodka dosing were the same thing. I’d prefer the fuge and macro algae myself.

  14. I am a firm supporter in natural is better. DSB in fuge with rock, and chaeto as well. Nitrates always under control and you dont have to “medicate” your tank for nutrient control. If I have to add something, I do it for corals only.

  15. Compy Ginorio

    I use a fuge with macro algae on a reverse light schedule. And also keep my ph in check at night.

  16. First saw the Blocks at MACNA Denver and love the fact they take up little room and have an enormous surface area.

    Also would like you to get some Turtle Grass for a planted SW tank.

    Keep up the good work!

  17. Kevin R Gravier

    I looked into making a diy macroalgae refugium for my biocube, it ended up not getting done, but this was very valuable info, specifically the Kelvin rating for the light.

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