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How do I get nitrates down?

nitrate removal

Part 1 – Marine Nitrate Removal

What are nitrates?

Nitrates are one of the natural by-products from the decomposition of fish waste. The original ammonia in the fish waste (highly toxic in itself) is broken down to form nitrites which in turn are converted to nitrates by the natural bacteria in the water. Each step of this reaction requires oxygen. In marine aquariums we are constantly striving to get lots of filtration and circulation to improve the environment for fish and invertebrates alike. This tends to create an oxygen rich environment which favours the quick and efficient conversion of ammonia to nitrite and nitrite to nitrate. So in short, modern aquariums are almost designed to produce high levels of nitrates.

Until recently water changes were thought to be the best way of getting rid of Nitrates.

Are water changes the answer to nitrate removal?

Water changes are an effective way of diluting pollution in your aquarium but they can be a long joyless method of trying to get rid of those pesky nitrates. Many people have commented on doing large water changes, testing the nitrates afterwards, seeing an improvement only to find the nitrates are back up again a few days later. In many cases nitrates only become a priority when they have been at a persistently high level for a long time.

Unfortunately nitrates get absorbed into the sand and the rock work very easily

So diluting nitrates in the water column by performing water changes means that more nitrates leach out of the sand or rock work,  bringing you back to square one again. One way to demonstrate this is to mix up a fresh batch of salt water and put in a good handful of sand or a piece of rock from your aquarium and in less than 24 hours a nitrate test will reveal levels almost as high as your aquarium.

Nitrate levels are a balance between nitrate production and nitrate removal.

What is the answer to nitrate removal?

The secret, if any, is to ensure the removal of nitrates in the aquarium is greater than the production of nitrates. This simple fact is what often leads to frustration, as you can follow all the rules and still look like you’re getting nowhere. If nitrate removal and production are equal the levels will remain the same. You can even tilt the equilibrium so that more nitrates are being consumed than produced but then nitrates start to leach out of the sand and rocks.

This is why nitrate reduction can be a slow process and the best course of action is to not allow them to accumulate in the first place.

Does anything eat Nitrates?

This article started off by saying nitrates are an end product. Under normal aquarium conditions nitrates accumulate as they cannot be converted into anything else. However in certain conditions nitrates can be broken down by bacteria to produce nitrogen gas. This is not an easy step, requiring extremely low oxygen levels, and in order to survive the bacteria removes the oxygen from nitrates. This is essentially how nitrate filters work, creating an enclosed anaerobic environment were the process takes place. It also occurs at the heart of every piece of live rock.

Living rock, we love it!

Some of the best aquariums around the world are filtered using live rock, a protein skimmer and little else. This shows the ultimate importance of both of these elements. The purpose of a biological filter media is to provide a large surface area for bacteria to colonise. Each piece of live rock possesses a massive surface area and acts as a perfect home for bacteria. Its external surface promotes aerobic bacteria that process ammonia and nitrites, whilst its interior surface promotes anaerobic bacteria that process nitrates. These two types of bacteria work hand in hand and can break down large quantities of fish waste as long as you take care of your live rock.

Live rock is all the biological filtration you will ever need.

Reducing nitrate production

Wash your food


When feeding frozen food it’s important to realise the freezing process is destructive. Legs pop off, juices flow out, and there can be a lot of waste built up in the frozen liquid around brine shrimp or mysis. Defrost your food in a cup of aquarium or RO water, give it a stir and then strain of the meaty bits, this way the fish only gets fed what they need.

Feed wisely

Watch how much you feed and make sure you feed good quality foods. Frozen foods are good quality but they can input more waste than you bargained for. Alternating frozen foods with a good quality flake food gives you the best of all worlds. Vitalis Marine Flake is designed to remain water-stable for longer than other foods on the market. In addition to it’s high digestibility this makes it one of, if not the lowest polluting food available. It is made from high quality, sustainably sourced ingredients and also has the right nutritional balance for your fish.

At Shirley Aquatics we get requests all the time to try out foods and never have we seen such an immediate response by the fish to dried food as we have with Vitalis, we feed our fish on it and suggest you do the same.

Part 2 – Tropical & Marine Nitrate Removal

Below are some more tips on reducing nitrate levels in a marine aquarium that some tropical fish keepers may also find useful.

Wash your filters

This might get people running and screaming, but in a marine aquarium you should wash any foams in your filter under tap water (ideally followed by a rinse in RO water) every week. This goes against everything fish keepers are told from the very first time they buy a goldfish. But in this situation we do not want the foams to grow bacteria, remember the live rock should do all the biological work. The foams should be used as mechanical filters only, catching particles from the water, excess food etc which then get flushed down the sink. No bacteria grow on the surface and therefore no nitrates are produced.

Remove biological media

Again this seems like another loony tunes suggestion but most biological filter media is too efficient. The high flow rates in external filters coupled with efficient biological media create effective nitrate producing machines, The bacteria that were growing happily on the live rock are seduced into moving into a new home in your hi tech filter media and lose their link with the anaerobic bacteria in the middle of the live rock.

As long as you have a sufficient amount of live rock in your tank the process should be relatively painless

You should plan to remove a few bioballs or ceramic rings every week or every other week to keep any disturbances to a minimum. It’s not a bad idea to keep an eye on your water quality whilst doing this.

Protein skimmers rule

If you haven’t already got one, get one! Their job is to remove raw sewage-like material straight from the aquarium. If your skimmer is stripping out lots of this gunk then the nitrite converting bacteria don’t even get a look in and you have reduced another area of nitrate production. Maintaining your skimmer is key, any sludge that builds up on the neck of the skimmer will dramatically reduce its performance as will any lime scale build up inside the pump or in the air intake.

In a healthy system with a correctly matched skimmer you should be getting between one and two cups of dark brown liquid a week. Aim to clean the cup and the neck once a week, whether they are full or not and look at cleaning the pump once a month. Also bear in mind water parameters can affect the performance of your skimmer, pH is a good example and maintaining it correctly keeps the skimmer at full throttle.

pH and KH can have an effect on the growth rate of bacteria so keep a close eye on both.

If you’re unsure where to start, here is an introductory video of the Reef Skim Pro range by TMC.

Better nitrate removal

This is often the more difficult side of the equation to accomplish, so make sure you have all of the methods of reducing nitrate production in place before hand.

Waft your rock

Everything so far should be telling you that live rock is the real champion in all this. It is important to keep this investment working in peak performance. To do so you need to get your hands wet and waft your hands over the rock work, you should see plumes of dust flying off. This is silt that blocks up the “pores” of the live rock and stops it from doing its job properly. Wafting cleans the live rock and transports the silt towards your filter were it can be dealt with.

Clean your bottom

Remember that the substrate can be at the root of many nitrate problems, so ensure that there is no detritus in or on the sand. In severe cases it may be an option to remove the sand all together and replace it with fresh sand once the nitrate levels are under control.

Full steam ahead

Increasing the flow rate in your aquarium can work wonders for reducing levels of organics including nitrates. Ideally you need to turn your tank volume over 20 to 30 times per hour, add up all the flow rates of the pumps and power heads (excluding protein skimmers) in your aquarium and see how close you get. Try to get a random flow dynamic going in the aquarium, use a wave maker or even change the position of your power heads on occasion.

By holding a power head and directing it over the rocks you can use it to “blow the cobwebs away” lifting detritus up and letting your filter deal with it.

Boosting your flow rate directly improves the health of your fish and corals, it also carries more of the waste that can build up in the aquarium to the filtration system. Less detritus clogging your live rock means it can work more efficiently and chew up nitrates at a faster rate.

Part 3 – Marine Nitrate Removal continued

The final part of the story includes more information on how to reduce nitrates in a marine aquarium.

You may have enough bacteria in your aquarium but are they working at their full potential?

Bacteria, nutrition and more

We are often reminded how important nutrition is to us, getting the right vitamins and minerals is vital to our health and well being. This is also true on a micro level for bacteria. Micronutrients are critical for the growth, reproduction and performance of filter bacteria, if they are all not present in the right levels the bacteria will not reach their full potential. Just as corals use and deplete levels such as calcium and strontium in your aquarium, bacteria do the same to the nutrients they require. If they need elements A, B and C to grow and there are limited amounts of C present in the aquarium it doesn’t matter how much of the other two are there the bacteria won’t get going until the correct balance of all three are there.

Companies are aware of the importance of micro nutrients and micro elements and have released products that provide the right balance, one of our favourites is Tropic Marin Elimi NP.

Tropic Marin Elimi NP is like Red Bull for bacteria and is excellent for giving them what they need. You will only need to use around 2-3ml per day so you should get a few month’s worth from your bottle depending on the size of your tank. For our shark tank we have to use half a litre a day! The manufacturer recommends that you get phosphates under control before starting the course as high phosphates and micro nutrients may result in algae problem.

The right kinds of bacteria for nitrate removal

We regularly hear about drinks that contain specific bacteria that help to promote a healthy digestive system. We already have bacteria present in our gut but it may be that these drinks contain a more efficient strain. The same is true in your aquarium.

Bacteria must be present to eliminate ammonia and nitrite, but are they the most efficient species?

Are they even the right type of bacteria to eliminate nitrates present? It would not be an easy task to find out, however, if you are suffering with high nitrates the chances are something isn’t right in this department. Saving the best product until last Eco labs have produced a unique product called Special Blend. This unique product contains a particular strain of photosynthetic bacteria which actively sets about the reduction of nitrates in the marine environment with some amazing results.

It can take up to six months to get certain biological pathways stable in your aquarium so why not add the right bacteria from day one?

Provide the right working environment!

From the very first time you look at a marine aquarium you are told how important it is to maintain the right conditions for these often delicate creatures, but who really looks after the water quality on a day-by-day, hour-by-hour basis? You guessed it, bacteria. Very little attention is paid to their specific needs and conditions.

The right media is essential for their success, live rock is the ultimate media but there are others you can add to any filter to increase nitrate removal. Most ceramic medias are too open plan as they allow highly oxygenated water to access all areas providing no slow flowing anaerobic areas for nitrate removal. Seachems Matrix and De Nitrate are two exceptional medias that are effectively artificial live rock and are a great help in the fight against nitrates.

Nitrate removal via filters

These are very effective ways of eliminating nitrates, but I would suggest using them only if you are already implementing the previous strategies and are still not getting the desired results. It’s often the case where, despite your best efforts, the fish are too greedy or you love your fish too much and have squeezed one or two too many into your aquarium. In this case nitrate filters are valuable tools and if set up correctly you can see the nitrates tumbling in a very short space of time. A nitrate filter may have 100ppm of nitrates going in and zero ppm on the way out, the down side is they can be costly and tricky to set up correctly.

No such thing as good algae?

One of the more natural methods of nitrate removal and one that has been used for decades is the use of macro algaes such as Caulerpa and Chaetomorpha. These thrive on nitrates as well as phosphates and, if managed correctly, will provide you with a nutrient poor reef, in other words mimic nature.

They need good flow rates as well as lots of lighting and they can take over if left to grow freely in your display tank which may damage corals. The best way to grow them is in a separate tank or sump called a refugium were they can be managed to greater effect. Many people employ a reverse photoperiod (switch the lights on over the algae when the main lights go off) this helps to reduce the daily pH swing you can get in a reef aquarium. The key to any macro algae farming is regular harvesting. The algae sucks up nitrates by growing. If it fills the tank or sump, growth slows down and so does nitrate removal. As a rule of thumb, the algae should grow vigorously enough for you to harvest 50% every two weeks.

Nitrate removal via chemical filtration

Whilst effective in its own way, this last group of nitrate removal methods is often the least economical. Methods of chemical removal act by absorbing nitrates. The down side to this is that once they are exhausted you have to add more. Many products such as polyfilters and Amquel are fantastic at absorbing or converting organics such as nitrates in emergencies but are a costly way of achieving your long term goal. They all have their uses but if you choose to base your method of nitrate control on the topics discussed so far you are likely to have a more reliable and self-sustaining system which ultimately means more time enjoying the marine hobby and less time working on it.

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