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
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
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.
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!