Friday, 20 July 2012


When most aquarists hear the word nitrates, what usually comes to mind is the whole “nitrogen cycle” thing. You remember this. Your fish take a poop and it breaks down into ammonia. Then the Nitrobacter and Nitrosonomas bacteria take over (which by the way, there is new evidence that proves these strains are NOT the ones responsible for the nitrogen cycle, so all those old books are now wrong). Ammonia is then converted to nitrite then finally to nitrate where it slowly accumulates and provides food for algae, turning your tank into a green mess.
Without any controls, nitrates go nowhere- they just accumulate. When concentrations hit 5 ppm or more, it can fuel film algae, hair algae, and cyanobacteria. In a reef tank, stony coral branches and polyps usually get covered by hair algae strands and film algae. This will harm and often bleach out sections of the coral. It’s not that grave of a situation in a fish-only setup because most marine fish can tolerate higher levels of nitrate. But you will still wind up with unsightly algae growing everywhere.
Not all the nitrates in your aquarium comes from the nitrogen cycle. Nitrates are added with food and with water changes. Many organisms in your aquarium produce nitrates directly. This has nothing to do with the nitrogen cycle.
Nitrate levels in aquariums are much higher than those in the ocean. The average nitrate levels of the ocean is 0.1 ppm at depths up to 50 meters, and 2.5 ppm and higher in deeper regions. But in the South Pacific reefs where we get most of the creatures we want to keep, nitrate levels average around 25 ppb (that’s parts per billion) which is equivalent to 0.025 ppm. So here’s the first problem: a typical hobby nitrate test kit can only go down to about 1.0 ppm, which is a nitrate level 40 times higher than what we’re shooting for. If you test for nitrates and the test vial looks crystal clear and colorless, your nitrate level could still be a hundred times higher than the ocean levels.

Why Nitrates Are Bad
Aside from getting nuisance algae, nitrates are not healthy for fish or invertebrates. Everyone says that fish are not affected by nitrates. This is not true. Nitrates are toxic to fish. They will die from nitrate poisoning at higher levels. Fortunately, lethal levels cannot be reached even in the most neglected marine aquarium. Nitrates to fish are like arsenic to humans. You will die from it at a certain dose, but at low concentrations you will live a full life, albeit not a healthy one.
At around 100 ppm of nitrate, many fish show signs of stress, color loss, and suppressed appetite. There is no evidence that this is caused by nitrates or sister compounds that concentrate in aquariums when nitrate levels are this high. Nevertheless, most experts recommend that fish-only tanks be kept at 10 ppm or less, with an absolute maximum level of 25 ppm.
Surprisingly, reef tanks and most corals need nitrates to survive. The zooxanthellae present in all photosynthetic corals are algae. They need nitrates to grow. But when nitrate levels are too high, it causes an explosion of the zooxanthellae population within the host coral and in turn, actually decreases the rate of growth of the coral. This begins to occur in some SPS corals when nitrate levels reach a low 0.5 – 0.7 ppm. LPS and many soft corals can tolerate 3-5 times this concentration with no ill effect. At 5.0 ppm and higher, nitrates become poison to many SPS corals. To make matters worse, high nitrates cause runaway film algae which covers the skeleton and polyps of these corals, exacerbating the problem.

Where Nitrates Come From
The number one source of nitrates is feeding. Most nitrates come from the proteins in uneaten fish food that metabolizes into ammonia. Fish that consume the food stop the decomposition to ammonia and break the cycle. In other words, fish excrement does not contain any nitrates. Fish will eliminate the nitrates for you, as long as everything you put in the tank gets eaten. Fish feces will decompose to ammonia, but the levels are far less intense than an equivalent weight of uneaten frozen fish food breaking down in the water.
I cringe when I see someone throw a frozen cube into an aquarium. The liquid from commercial frozen fish food cubes contains food particles too small for fish to eat. It just decomposes into nitrates. In fact, the packing juices contain more nitrogen compounds than the food itself. It is important to defrost and rinse frozen fish food through a net before feeding. If you have a persistent algae problem, this could be the answer.
Feeding corals is more prone to nitrate production than feeding fish. Target feeding helps concentrate foods at the coral, but most of it winds up in the water column to decompose. The worst feeding technique is to dump filter feeding foods directly into the tank. A very small percentage may arrive at a polyp, and the rest just fouls the tank. But PLEASE- don’t stop feeding your corals for fear of elevated nitrates. There is no additive in the world like food to give your corals extended polyps, better coloration, and an overall healthy appearance. You need to balance nitrates from food with effective ways to remove it.
Another source of nitrates are microscopic life forms that are constantly dying in your tank and decomposing. There isn’t much you can do to reduce this source of nitrates, but keeping ORP and PH high will speed the denitrification process. Of course, the death of a major organism like a fish or coral will cause a much greater nitrate spike. Don’t ever let a specimen “decompose to nothing” in your aquarium. Besides nitrates, other toxins and organic compounds are produced that will take a long time for your tank to recover.
Another source of nitrates is make up water. The US federal government allows up to 44 ppm of nitrates in drinking water from municipal sources. If you’re on a well, nitrate levels are not regulated at all. This could be a significant source of nitrates in your aquarium. Ask your water company for a free water analysis report. I don’t recommend testing your tap water yourself using your aquarium nitrate test kit because of the limitations in low level accuracy.
You don’t need a reverse-osmosis unit to remove nitrates, just a deionizing filter. Products such as the Aquarium Pharmaceuticals Tap Water Purifier works well. You can also purchase water from RO/DI machines found outside of major supermarkets and department stores. RO/DI water is the best defense you can have against nutrients, heavy metals, dissolved organics, and other compounds that wreak havoc in an established aquarium.

How to Get Rid Of Nitrates
Before we had high tech equipment and fancy chemical additives, most aquarists used water changes to dilute nitrates. For moderately stocked tanks, this is still the best defense to keep nitrates under control. In addition, measuring nitrate levels is a great way to tell when a water change is due. Choose a goal of say 5 ppm. Test your tank regularly. When nitrates reach your goal, it’s time for a water change.
If your tank is heavily stocked with fish and/or corals, water changes alone may not be able to keep up with nitrate production. You will need to supplement water changes with some form of biological or chemical control. Here’s a list of common nitrate reduction methods that can help rid your tank of nitrates:
Live Rock This is the most inexpensive nitrate reactor on the market. It comes free when you buy a piece of live rock. The internal “nooks and crannies” harbor bacteria that are forced to live in anoxic (oxygen poor) conditions. The bacteria reduce nitrates to nitrogen gas. The only drawback to live rock nitrate reduction is that the filtering capacity is very weak. Even with strong tank circulation, 50 pounds of live rock may be able to process only 2-3 ppm of nitrates daily.lr2.jpg

Macroalgae – All algae, including macroalgae feed on nitrates. It is has been found that Caulerpa sp. Prefer to feed directly on ammonia. The good news is Caulerpa will prevent some of the ammonia in the tank from becoming nitrates. The bad news is that adding lots of Caulerpa won’t necessarily reduce existing nitrates. Still, any macroalgae in the tank will certainly help reduce nitrates and phosphates. Macroalgae also competes well against hair and film algae, minimizing its growth.
Algae Scrubbers – These devices have been used in public aquariums for years. They consist of plates that are sprayed with tank water and exposed to bright lighting. All forms of algae grow on the plates. The plates are periodically removed and the algae is cleaned off and discarded. While very effective, the typical home aquarist doesn’t have the room for this kind of setup. A less effective but adequate alternative is to use a refugium where various algae can grow undisturbed and be harvested regularly.
Protein Skimmers – A quality skimmer can remove ammonia, nitrites, and nitrates directly. The whole concept of the Berlin method is to combine live rock with a large aggressive skimmer as the only means of filtration. Such a setup is a powerful combination to combat the constant build up of nitrates. Many aquarists fail to get the Berlin Method to work for them, simply because they employ an entry level, poorly designed skimmer that does little more than aerate the water.
Deep Sand Bed – Deep sand beds make excellent nitrate reactors. The way they work is that the deepest portions of the gravel do not receive replenished oxygenated water and become anoxic. This causes the bacteria to use a nitrogen molecule as an electron receptor instead of an oxygen molecule, and the result is the bacteria electrically transform the nitrate molecule (NO3) into nitrogen gas (N2). The gas is partially dissolved in seawater but then is quickly released into the atmosphere as it hits the water surface.
DSB’s are extremely efficient nitrate reactors and can handle very large loads, perhaps 5-10 times greater than live rock alone. In-tank DSB’s have lost popularity due to misunderstood maintenance practices. Modern day DSB’s place the sand bed external to the display tank. These are typically DIY units made from deep containers (i.e., a Rubbermaid trash can) filled with sand and drilled with two bulkheads on opposite sides of the top of the container. Water passes over the top of the gravel bed just like an in-tank DSB. Nitrates permeate to the bottom of the gravel bed and are assimilated by anaerobes.
Coil Denitrators – These units used to be very popular 10-15 years ago, They are simple to build and easy to operate. I believe their popularity has waned due to DSB’s appearing in the late 80′s.
Basically, coil denitrators consist of a long coil of tubing (for example, a 100 ft roll of airline tubing). The end of the tubing goes inside an air tight chamber containing bioballs or other material with lots of surface area. The way they work is this. Aquarium water is slowly pumped through the tubing. By the time the water reaches the end all the oxygen has been consumed by bacteria growing on the inside walls of the tubing. The water then drips out over the bioballs that are covered with anaerobic bacteria.aquamedic.jpg

To increase the efficiency of coil denitrators, you need to feed the bacteria with a carbon source such as methanol, sugar/glucose, or vodka. Commercial units let you add the food directly to the inner chamber containing the bioballs. Some units contain specially made bioballs (I.e., Deni-Balls) that are filled with carbon food. For DIY, you can just dose the tank directly. I built my own coil denitrator several years back and was amazed how well it worked on a heavily stocked fish aquarium. However, one time I accidentally turned the valve open too much and let the water rush through the tubing. Within seconds all the anaerobic bacteria in the center chamber died (oxygen kills anaerobes). I pretty much had to wait a month for the denitrator to cycle again before it would start removing nitrates.
Chemical Nitrate Reduction – Chemical nitrate removers have been around a long time. Zeolite is a 50 year old product used in freshwater aquariums (and kitty litter) that adsorbs ammonia and other forms of nitrogen. It doesn’t work well in saltwater because of the complex ions that saturate the media very quickly. Carbon removes some nitrates, though it is much better at removing organic compounds. Products such as Chemi-Pure, Polyfilter, and Purigen do a good job of removing nitrates.
Probably the best product for nitrate removal today is an additive called AZ-NO3 (Absolute Zero Nitrates). I’ve used AZ-NO3 several times in problem tanks where algae has gotten out of control. The results are nothing short of amazing. I call this product the “second chance” additive, because it will turn the clock back to the day you first setup your tank. Within a month of the first dose, you will see pure white gravel, ultra clear water, no film or hair algae anywhere, plus the cleanest looking live rock imaginable. AZNO3 is an expensive product so you wouldn’t want to use it continuously. But to get a fresh start on a dirty tank, it can’t be beat. I urge every to try AZNO3 at least once. If for nothing else, just to see the remarkable effects of zero nitrates in your own aquarium.
Bio Blocks – There exists a continuing misconception in this hobby that bioballs are “nitrate factories”. The fact of the matter is that the same amount of decomposition occurs in your aquarium whether bioballs are present or not. The exact amount of nitrates are produced either way. The problem with bioballs is that nitrates are produced on the bioball surfaces, then they must find their way to the place where the denitrifiers live. In most setups this is the inside surface areas of live rock. When nitrate is produced in high concentrations on the surface of live rock, it is more likely to diffuse in situ to the deeper portions of the rock where in can be turned into nitrogen gas. Bioball-generated nitrates simply miss out on the opportunity to be converted because it can’t find the denitrators.
Other media with large surface areas such as Bio-wheels and even filter pads work the same way. It is important to replace mechanical filtering pads or filter bags frequently (at least once a month) to prevent them from becoming efficient biological filters. Even old activated carbon will harbor nitrifying bacteria once the carbon is exhausted and the pore structure becomes filled with organics.
To overcome these problems, people have tried different things to replace bio media. One alternative is to fill the wet/dry chamber with live rock rubble. As long as it stays wet from the trickling water flow, the rock remains viable even though portions of it are out of water. But because live rock is a weak filter, you can never achieve the same filtering capacity as bioballs. There are several new products on the market that overcome this. They provide areas for both nitrifying and denitrifying bacteria in the same media. The Cell Pore product is made from ceramic that has been heated to a molten state and then heavily aerated as it cools, which turns it into a sort of “foam” rock. It contains thousands of holes and deep crevices- a similar structure to natural live rock.

Water trickles over the material and provides biological filtration on the surface while the deeper pores harbor denitrifiers to eliminate nitrates. For most setups with moderate to heavy bioloads, this product can’t be beat.
Sulfur Denitrator- Sulfur filters have typically been used in public aquariums but only recently have become popular in the home. They consist of a recirculating canister and input/output drip lines similar to a calcium reactor. The canister is filled with elemental sulfur in the form of small beads. Bacteria feed on the sulfur and in the process convert nitrates to nitrogen gas. These filters need to be cycled just like a new tank. They require a month or so to grow sufficient bacterial colonies on the surface of the beads before they operate. The effluent water from a sulfur filter can become quite acidic, so most units pass the water through an aragonite bed before returning it to the tank. In a sense, you get a free calcium reactor. But I suspect the amount of dissolved calcium and carbonates in the effluent is too low to make much of a difference.
I have just started experimenting with a sulfur filter, an H&S Model 110SR that was loaned to me by Eric Edwards of FinsReef ( Once cycled, I will certainly publish my findings.


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