Natural seawater, as found in our oceans worldwide, contains just about every known element on the earth. For those of us who collect this natural resource and utilise it in our home reef tanks, voila we too, have just about every known element on earth in our home aquarium.

Others of us will prefer to make synthetic salt water, where manufacturers will artificially select the chemical make-up of that salt choosing which elements are contained within it and how much of them.

There are a variety of different elements contained within our saltwater mixes that are beneficial to our reef tank inhabitants, i.e. fish, corals invertebrates etc. Calcium, Magnesium, and Alkalinity are what most people think of when we mention elements but did you know accumulations of certain elements are unwanted and undesirable in our aquariums? Some synthetic salt manufacturers even chose to deliberately leave out undesirable trace elements present in NSW over bioaccumulation concerns; especially when the elements are not seen to be beneficial to reef keepers.

Two things manufacturers definitely aim to eliminate are Phosphates and Nitrates. These can be the bane of many reef keepers lives, constantly struggling with rising or fluctuating levels of either.

Nitrate is an organic compound (or polyatomic ion – if you are scientifically minded) comprised of 2 elements, Nitrogen (N) and Oxygen (O). One single atom of Nitrogen and three atoms of Oxygen are formed together to create Nitrate, often referred to by hobbyists as its molecular form NO3. The NO3 abbreviation shows us how many of each element is contained within that compound. N on its own means there is 1 atom of Nitrogen and O3 means there are 3 atoms of Oxygen.

Nitrate is toxic to aquatic life, but only in high concentrations. As long as we work to keep this compound at low levels it should cause no issues.

Nitrates are a by-product of the nitrogen cycle caused by the breakdown of waste and debris to ammonia. Ammonia being 100x more toxic than Nitrites is detoxified by bacterial oxidisation (i.e. the addition of oxygen) to Nitrite NO2 and then ultimately to Nitrate NO3. As this organic waste continues to break down in your tank, the nitrate continues to creep up. This can further be exacerbated by overfeeding fish and corals or by poor maintenance procedures i.e. allowing waste to accumulate without removal.

In home aquariums Nitrate is measured in parts per million, PPM. Anything below 50PPM is considered safe albeit hobbyists aiming for hard coral stocked tanks (SPS & LPS) may need to aim for a figure well below this. This said I have personally seen tanks reach great success at ULNS level (ultra-low nutrient system) i.e. Nitrate less than 1PPM and also with tanks hovering around that 50PPM range. Stability is likely most important here but hobbyists should aim to keep the levels low. Whilst there is a desired level that we as hobbyists aim for (5ppm and below) every aquarium is different and will respond in different ways to varying nutrient levels.

Phosphate is an organic chemical derived from the element Phosphorus. It is comprised of one single atom of Phosphorus (P) and four atoms of Oxygen (O) and often referred to by hobbyists in its molecular form PO4. The molecular PO4 abbreviation again shows us how many of each element is contained within that compound. P on its own means there is 1 atom of Phosphorus and O4 means there are 4 atoms of Oxygen.

Phosphate is also produced from excess fish

waste and food, but it can also come from poor water quality. It’s important that we use 000 TDS RODI water when topping up our tanks or when mixing water for a water change. This will prevent us from adding phosphates into our aquariums at its source.

Phosphates are often considered to be the main ‘baddie’ in play when dealing with nuisance and pest algae and whilst this is true to some degree it’s not the only factor in play. Excess levels of Phosphate will allow for algae growth and it will also inhibit calcification in corals. Insufficient phosphate will prevent algae from growing but it will also starve your corals of nutrients and kill them.

In home aquariums Phosphate is also measured in parts per million, PPM. Anything between 0.03PPM and 0.07PPM are considered the ideal range but I have again seen success with tanks running as low as 0.01PPM and as high as 0.5PPM. Much like with nitrates stability is most important here but hobbyists should aim to keep the levels low.

Testing of these 2 aquarium ‘baddies’ should become ritual to any hobbyist and their control and management of these test results will ultimately lead to the success or failure of a home reef aquarium.

Both Nitrates and Phosphates can be tested for in our aquarium water using a wide range of home test kits. Digital kits like the Hanna Checkers can be used for those who struggle reading colour charts and Titration type tests can be conducted for those who do not mind the colour charts. In more recent years ICP testing has become more accessible allowing for a more comprehensive lab analysis to those that require it.

Given that we now know that too little of either compound is bad for our aquariums and may cause corals to starve and die, and we also know that too much of it may also be bad with many other ill effects, how can we remove excess nutrients and get our Nitrates and Phosphates back to a safe level.

There are a number of different methods or ways to remove excess nutrients from our aquariums. Ultimately each hobbyist will have their own preference on method. Some may prefer a natural approach; other may prefer to use chemical medias.  There is no right or wrong way and some methods will work better for some rather than others. Ultimately my advice would be to encourage hobbyists to achieve stability. Nothing good happens quickly and unless your nutrients are an emergency a sensibly paced reduction wont shock the tanks inhabitants and allow the inhabitants to adjust to the conditions.

The easiest way to remove Nitrates, Phosphates and in actual fact any unwanted element or nutrient is by dilution. Dilute the water in which the nutrients are bound and you’ll have less of that nutrient. Imagine a glass of Coca Cola. If you remove 10% of that Cola and replace it with 10% of fresh tap water, it will be a weaker glass of coke. If you continually remove 10% of that coke every hour and add 10% of fresh water, eventually, the glass will be full entirely of fresh tap water.

Aquariums work the same way, and so water changes with fresh salt water are probably the most common and also most effective way of removing the nutrients. Be mindful that large water changes can affect the other elements in the tank and as we strive for stability a series of smaller changes may be more beneficial to one large change.

A lower fish stocking or maybe even a reduction of feeding may be sensible. If your tank is producing more waste than you can cope with, you have too many fish, consider removing some! Equally if you’re a liberal feeder and known to overfeed cut back a fraction. Feeding frequent small feeds are more beneficial to one large feed each day.

Carbon dosing with products like Red Seas NO3PO4X, Vinegar or Vodka may dramatically reduce excess nutrients. Carbon dosing will aid in the propagation of denitrifying bacteria that convert Nitrate into Nitrogen gas. It is important when using a carbon dose method that you ensure the water is well oxygenated and a protein skimmer can help with this. Many people combine the use of carbon dosing with media like Sera Siporax to provide a deep low oxygenated zone for these bacteria to multiply and consume nitrate. Whilst it isn’t essential it will often see improved results.

Protein Skimmers are found in almost all reef tanks and what a wonderful job they do! A technique used in water treatment facilities and public aquariums initially, Foam Fractioning or Skimming as we call it, removes organic compounds, food and waste particles from the water column. Have you ever sniffed the protein skimmate removed from your aquarium? Have you ever taken note of the foul colour or consistency of that waste? How many of you honestly would rather that waste stayed in your tank as opposed to inside the skimmer cup waiting to be removed entirely? Many people will opt to run a reef tank without a skimmer but my personal preference would be to use one based upon what I’ve seen mine removing. If my tank needs excess nutrients I’d rather add it in a controlled feed than allow already decomposed waste to sit in the water column.

How about a refugium or algae bed? Growing algae’s in a refugium separate to the main aquarium display and using a dedicated light can have many benefits. Firstly, those algae consume the nutrients within the water column to grow. They absorb the Phosphates and Nitrates removing them from our tanks. We can then harvest the algae and allow it to regrow by absorbing more Nitrate and Phosphate. Magic! In lighting this algae without dedicated light, we can also achieve a more stable overall tank PH. It also provides a safe haven for varying pods like copepods or amphipods to repopulate, these of course ultimately making their way to the main aquarium and becoming free fish food! So not just a nutrient removal but also many other benefits.

Bio Pellets are a reasonably new addition to reef keeping but another way of maintaining low nutrients. They are small plastic bio gradable beads that are a source of organic carbon. These beads are fluidised in a media reactor allowing them to break down and in the process uptake dissolved nutrients in the water column, i.e Phosphates and Nitrates. This method can take a bit longer to ‘get started’ as the concentration of media cannot be added all in one go. The media also needs replenishing at varying intervals as it breaks down.

Algae scrubbers are another popular method. Very similar to algae refugiums except this time aquarium water is passed over a mesh screen in an area separate to the main display. This screen is then lit by a dedicated light encouraging algae to grow upon it. The theory here being that if algae grows on the screen, it won’t grow elsewhere in the aquarium and whilst it grows it’s removing those unwanted nitrates and phosphates from the water column!

Ultimately there are a vast number of ways of exporting nutrients from your aquarium and we have only covered some of the most popular, but the important point to make is all methods will serve each hobbyist differently. Ultimately, we all have a preference as to which will work best for us. Just because hobbyist A prefers method 1 and hobbyist B prefers method 2 doesn’t make one more successful than the other. Each method will have pros and cons and as the hobbyist it’s up to you to decide which is most important to you.

It is worth remembering that appointing too many of these methods at once may be counterproductive. I often see people utilising algae beds AND trying to use NO3PO4X or similar at the same time. You now have competing methods trying to utilise the same Phosphate and Nitrate in the water. This doesn’t make them twice as affective, but it means they fight for dominance while the Phosphate and Nitrate skip merrily along continually increasing!

Taking nutrient removal to a more advanced yet still incredibly important stage we also need to ensure we try to adhere to something called the Redfield Ratio. For those interested its named the Redfield Ratio as it was discovered by a gentleman named Alfred Redfield in 1934 whilst studying Nitrate & Phosphate data in the Atlantic, Indian & Pacific Ocean.

The Redfield Ratio is the ratio of Carbon, Nitrogen and Phosphorus found throughout the ocean in Natural Seawater. It is comprised of an atomic ratio of 106:16:1. 106 moles of Carbon atoms, 16 moles of Nitrogen atoms and 1 mole of Phosphorus atoms. To help you better understand the measurement of moles, if you imagine a single atom was 1 egg, then a mole would be like having a whole carton of eggs.

When we refer to Carbon, we aren’t measuring how much activated carbon we are using here within our aquariums filtration, so do not confuse the 2. The Carbon aspect of the Redfield Ratio refers to its content within Natural Seawater as an element in its own right.

Typically, as reef hobbyists we do not look at the level of Carbon as an element within our reef tanks and so for the Redfield Ratio we are only focussed on Nitrogen & Phosphorus.

Maintaining the ratio is as simple as ensuring you have enough Nitrogen moles to Phosphorus moles. For every 1 Phosphorus mole, you’ll need 16 Nitrogen ones. Obviously, we do not measure our aquariums in moles and so the illustration pictured will help you to find an optimum balance. Some hobbyists will disagree with this chart and its context, others use it as a guide. Ultimately as a hobbyist the desire to follow it is up to you but in my opinion, it provides us with a useful visual aid.


If the Redfield Ratio is not maintained you will be at risk of forming varying types of algae. If however the ratio is maintained, you will develop far less risk of unwanted algae’s appearing.  This may be more difficult to achieve with certain nutrient export methods that uptake both Nitrates and Phosphates at once but at different rates. Refugiums growing macro algae’s may consume one nutrient faster than the other thus leaving more of one nutrient in the water column. This can then lead to algae outbreaks. This is why sometimes when you remove all or too much of one nutrient with the other still in excess, your aquarium can become unsightly with algae leaving you scratching your head.

In some instances, reef hobbyists may even need to dose extra Nitrate or Phosphate, in order to bring the Redfield Ratio level back into balance.

There are equally plenty of instances where hobbyists will have much greater numbers of one nutrient over another and everything will remain harmonious within their reef aquarium despite this unbalance, so see this as more of a guide than a hard and fast rule.

As a lifelong adult hobbyist, making it almost 15 years in the making, Danny has been keeping Saltwater for quite some time. As one of the biggest passions in his life in 2014 he combined that with his second biggest passion, photography and videography.