Nitrates are relatively harmless and midrange levels are nothing to be too alarmed about. Ideally, though, we’d like to keep them under 20 ppm for seahorses, and if you will be keeping live corals in your aquarium, and you’ll want to keep the nitrite since low as possible. Here is some additional information on nitrification and denitrification from my new book that explains where nitrates come from, followed by some suggestions on how to reduce them.
The amount of nitrate that accumulates in your aquarium is related to how much nitrification and denitrification your system provides. Nitrification is the process by which aerobic (oxygen loving) nitrifying bacteria break down toxic ammonia to relative harmless nitrate in a series of steps. Nitrification thus ultimately causes nitrate to build up in an aquarium. Denitrification is the process by which anaerobic (oxygen hating) denitrifying bacteria then convert nitrate into completely harmless nitrogen (N2), which eventually leaves the aquarium. Denitrification thus removes nitrate from your system. This entire process is known as the nitrogen cycle.
Cycling your aquarium simply means to build up a healthy population of beneficial bacteria in your tank that can carry out the nitrogen cycle and breakdown your fishes’ waste products. Ammonia (NH3), nitrite (NO2), and nitrate (NO3) are all nitrogenous (nitrogen containing) wastes. All living aquarium animals whether they be fish or invertebrates excrete these wastes, and they are also produced by the decay of protein-containing organic matter (uneaten food, detritus, dead fish or inverts, etc.). The nitrogen cycle breaks down these wastes in a series of steps into nitrogen gas (N2) which leaves the aquarium as bubbles.
The nitrogen cycle begins with ammonia, which is highly poisonous. In the first step of the cycle, Nitrosomonas bacteria reduce ammonia to nitrite, which is also very toxic. In the second step of the nitrogen cycle, Nitrobacter bacteria convert the nitrite to nitrate, which is relatively harmless but becomes harmful when it accumulates in high enough levels. In the third and final step of the cycle, denitrifying bacteria then convert the nitrate into completely harmless N2, which of course bubbles out of the tank as nitrogen gas. In this way, thanks to the nitrogen cycle, dangerous wastes are converted into progressively less harmful compounds and finally removed from the aquarium altogether.
When we set up a new aquarium, and wait for it to cycle, we are simply allowing a big enough population of these different types of bacteria to build up in the biofilter to break down all of the wastes that will be produced when the aquarium is stocked. If we don’t wait long enough for the cycle to complete itself and the biofiltration to become fully established, and hastily add too many specimens to a new aquarium too soon, they will die from ammonia poisoning or nitrite toxicity. This is such a common mistake among us impatient aquarists, that when fish get sick and/or die from ammonia/ntrite poisoning, it is commonly called the "new tank syndrome."
When your aquarium has completely cycled, the ammonia levels will stay at zero because, now that your biofilter is fully established, there is a large enough population of aerobic (oxygen loving) nitrifying Nitrosomonas bacteria to reduce all of the ammonia to nitrite as fast as the ammonia is being produced. The nitrite levels will likewise stay at zero because there is also a large enough population of aerobic (oxygen loving) nitrifying Nitrobacter bacteria to convert all of the nitrite to nitrate as fast as the nitrite is being produced.
The nitrate levels ordinarily continue to build up, however, because there are simply not enough anaerobic (oxygen hating) denitrifying bacteria to convert all of the nitrate that’s being produced into nitrogen (N2). Since nitrates are being produced faster than they can be transformed to nitrogen, the excess nitrates accumulate steadily in your aquarium.
That’s perfectly normal, since the denitrifying bacteria that carry out that final step, the conversion of nitrate (NO3) to nitrogen (N2), are anaerobes that can only exist in the absence of oxygen. For our aquariums to support life, and for the fish and invertebrates to breathe and survive, our tanks must be well aerated and well circulated so that there’s plenty of dissolved oxygen in the water at all times. That means there are normally very few areas in our aquariums where anaerobic denitrifying bacteria can survive, limiting their population accordingly (which is generally good, since some anaerobes produce deadly hydrogen sulfide gas during the decay of organic matter and would poison our tanks if allowed to proliferate).
Consequently, most aquariums lack a sufficient population of anaerobic denitrifying bacteria to complete the nitrogen cycle and convert nitrate to nitrogen as fast as the nitrates are being produced. The only way to keep the nitrates from building up to harmful levels in such setups is with regular water changes and by harvesting Caulerpa or other macroalgae periodically after it has utilized nitrates for growth. Overcrowding, overfeeding, or under filtration exacerbate the problem by resulting in more nitrates being produced and more frequent water changes being required to control the nitrate levels.
Live rock helps because the oxygen-poor interior of the rock allows anaerobic denitrifying bacteria to grow and break down nitrates. A deep live sand bed (DLSB) also helps because anaerobic denitrifying bacteria can flourish and break down nitrates at a certain depth below the sand where oxygenated water no longer penetrates, but a DLSB can sometimes be difficult to set up and manage properly if you’re inexperienced with live sand. Both live rock and deep live sand beds give aquaria denitrification ability — the ability to complete the cycle and convert nitrate to harmless nitrogen. Ordinarily, about 1-2 pounds of live rock per gallon is recommended – that amount of LR will provide your aquarium with all of the biofiltration you need, as well as adequate denitrification ability. You will then keep nitrates at harmless levels by performing regular water changes, harvesting Caulerpa macroalgae periodically, and good aquarium management.
So, Jen, nitrate is simply the end product of the process of nitrification, formed during the Nitrogen Cycle by the oxidation of nitrite by aerobic bacteria. Nitrates always tend to build up in a system over time, sometimes in sneaky ways you wouldn’t expect. For example, here is an article from Thiel Aqua Tech that discusses some of the hidden ways nitrate can enter your system:
Click here: No nitrate, removal nitrate, denitrating, denitration
Good ways to reduce nitrates in your aquarium therefore include adding more live rock, installing a deep live sand bed (preferably in a sump), installing a protein skimmer on your tank if your not already using one, and growing and harvesting fast-growing macroalgae such as Caulerpa.
Protein skimmers help reduce nitrates by removing dissolved organics from the water before they can enter the nitrogen cycle. The majority of the undesirable metabolites, organic wastes and excess nutrients that accumulate in our aquariums and degrade water quality are "surface-active," meaning they are attracted to and collect near the surface of a gas-liquid interface. Skimmers take advantage of this fact by using a column of very fine air bubbles mixed with aquarium water to trap dissolved organics and remove them from our systems. This air-water mixture is lighter than the surrounding aquarium and rises up the column of the skimmer until the foam eventually spills into a special collection cup atop the skimmer, which can be removed and emptied as needed. Proteins and other organic molecules, waste products, uneaten food and excess nutrients, and a host of other undesirable compounds stick to the surface of the bubbles and are carried away along with the foam and removed from the aquarium. As a result of this process, these purification devices are typically known as foam separators, foam fractionators, air-strippers, or simply protein skimmers.
In my experience, nothing improves water quality like a good protein skimmer. They provides many benefits for a seahorse setup, including efficient nutrient export, reducing the effective bioload, and increasing both the Redox potential and dissolved oxygen levels in the water. They do a tremendous job of removing excess organics from the aquarium, including phenols, albumin, dissolved organic acids, and chromophoric (color causing) compounds. Their ability to remove dissolved wastes BEFORE they have a chance to break down and degrade water quality makes them indispensable for controlling nuisance algae. A good protein skimmer is an invaluable piece of equipment for keeping your nitrates low and your water quality high when feeding a whole herd of these sloppy eaters in a closed-system aquarium.
I also like the use of macroalgaes for controlling nitrate and nuisance algae, Jen. Macroalgae use nitrate for growth just like plant fertilizer and pruning the macros regularly is a good way to export nitrate from your system. However, if the macros die in your system, they’ll release the nitrate they’ve consumed back into the aquarium. Fast-growing Caulerpa needs to be pruned properly to prevent vegetative events and avoid this from happening, as discussed below:
Macroalgae act as an excellent form of natural filtration, reducing the available levels of phosphates and nitrites/nitrates. Be sure to prune and trim back the fast-growing Caulerpa regularly; when you remove the clippings, you’re exporting phosphates, nitrates and other nutrients from the tank, thereby helping to maintain good water quality, and pruning the runners helps keep it from going sexual.
When pruning or trimming back macroalgae, take care not to actually cut it. Remember, you’re not pruning hedges or trimming trees — the idea is to carefully pull up and remove continuous, unbroken fronds. Simply thin out the colony of excess strands, gently plucking up convenient fronds that can be readily removed intact. A little breakage is fine, but cutting or breaking too many strands will result in leaching undesirable substances into the aquarium water as the Caulerpa lifeblood drains away. Too much cutting or breaking can thus sap the colony’s strength and cause die offs or trigger the dreaded vegetative events that judicious pruning otherwise prevents.
Another product I like for removing excess ammonia, nitrite, and nitrate is the Poly-Filter Pad (by Poly-Bio-Marine) Here is a product review on Poly Filters that touches on some good ways to use them:
Click here: Saltwater Aquariums Product Review – Poly-Bio-Marine Inc. – Poly Filter Pad
Finally, commercially made denitrators (special filters housing a large population of anaerobic denitrifying bacteria) are also available. They do a tremendous job of controlling nitrates but are rather expensive and tend to be high maintenance, often requiring regular "feeding" and carefully controlled flow rates to operate properly.
In summary, some of the measures that will help control nitrates in the aquarium are the following:
1) Make sure your protein skimmer is working correctly. A protein skimmer works 24 hours a day to remove excess waste and nutrients from a tank. If the venturi is clogged on a venturi skimmer or there is another problem with other skimmer designs, waste will not be exported from your tank and algae will take advantage of the waste.
2) Perform regular water changes. Regular water changes will decrease the level of wastes and nutrients in the water. But the water changes won’t do much good if your tap water itself contains phosphates and amines. Depending on how high the nitrate levels become, increasingthe proportion of water that you change each time may be necessary to help reduce those nitrates. There is an article about nitrate reduction at http://www.about.com/ in the saltwater section that really explains water changes (gives you the math), on actually how little you are reducing nitrates with small water changes when you have high nitrates.
3) Make sure makeup water is pure. Phosphates and nitrates often found in tap water. Phosphate and nitrate test kits will show if your tap water is contributing to your algae problem. If phosphate and nitrate levels are more than 0 ppm (some tap water measures out at over 50 ppm nitrate), filter the water through a RO/DI unit before using it as makeup freshwater or as source water for saltwater changes, or purchase RO water from a vendor.
4) Add additional detritivores to your cleanup crew. If excess food isn’t eaten, it will decay and add to the nutrients and waste in the tank. More microhermit crabs, Nassarius snails and cleaner shrimp will help ferret out any uneaten Mysis before it breaks down and enters the nitrogen cycle to eventually end up as excess nitrate.
5) Introduce macroalgae to consume excess nutrients and nitrates. If regular pruning is done, fast-growing Caulerpa will maintain its color and high growth rates without going sexual.
6) Chemical controls. Poly Filter pads can help absorb excess nitrates, changing color as it does so, which helps indicate= when the Poly Filter needs to be changed.
7) Controlled addition of food to tank. Don’t broadcast feed, scattering Mysis throughout the tank. Instead, target feed your seahorses or use a feeding station. Don’t overfeed, cleanup leftovers promptly, and observe fast days religiously.
In my experience, Jen, you shouldn’t have any trouble keeping nitrates under control with a Bio-Wheel filter as long as you practice proper aquarium management and maintenance and observe the sorts of precautions outlined above.
Best of luck with your new seahorse setup, Jen!