Nitrate – The Ongoing Problem

I answer numbers of questions concerning various aspects of marine aquarium keeping. Looking at the subjects of all these questions it seems one of the biggest problems that is faced by aquarists is excessive nitrate (NO3). If it is not a problem the subject seems to puzzle some.

It may be thought that I tire of the same question, but this is not so. Rather, I am pleased as it shows that aquarists are concerned about the welfare of their livestock and wish to understand how the problem could have arisen and how it could be dealt with.

Why are aquarists so concerned about nitrate levels? Probably because, along with phosphate (PO4), it is a known nutrient of nuisance algae, the horrible stuff that can show its ugly presence under certain circumstances. In addition, corals will tolerate nitrate badly in many cases, and in a lesser way the same can apply to fish.

I hope I will be forgiven for not repeating what is already in other articles on this website (or maybe I’m just lazy!). What I have done is note in brackets any relevant article and the path to it.

To get to ‘Articles’ simply click on the word at the top of the page or click the link.

First of all, nitrate is not a disaster in itself, in the way that a presence of ammonia (NH3) or nitrite (NO2) could be. Nitrate is a product of the so-called Nitrogen Cycle (see article ‘The Nitrogen Cycle‘ under the sub-heading ‘Filtration‘). The nitrogen cycle should be understood by all aquarists and is straightforward.

Nitrate will be produced in any marine system, the level being dependant on more than one factor – these include type of system, stocking level, and bio-filtration method. In addition, husbandry expertise should be included. Excessive nitrate levels are usually faced by new aquarists where experience has not had time to accrue, but the problem is not entirely restricted to the beginner.

First of all, how much nitrate is acceptable? There are guidelines of course, but it should be noted that an inability to meet the guideline does not mean disaster. However, a continuing effort to control the nitrate level to the guideline should be made (see article ‘Guideline Water Parameters‘ under the sub-heading ‘Water Quality’). For nitrate in a reef system, the guideline is 10ppm (parts per million) or less, and in a fish only system the same if possible, or as close to it as can be achieved.

It has been said that ‘the answer to pollution is dilution.’ This is correct for nitrate and the marine aquarium. Routine seawater changes should be carried out whether there is a nitrate presence or not, and the guideline is 10% of the total net system gallonage per week. This can be flexed somewhat according to need, but gives a base for a newcomer. In a well designed system that is not overstocked this in itself could be sufficient to control nitrate levels, where there are no other controls present.

To help prevent unwanted pollutants including nitrate getting into the aquarium, it is highly recommended that reverse osmosis water (‘super filtered’ tap water) is used. An aquarist could be surprised at the content of tap water (see article ‘Reverse Osmosis‘ under the sub-heading ’The Basics‘. Also see article ‘Should You Use Tap Water?‘ under the sub-heading ‘Water Quality‘). Reverse osmosis water should be used for the initial aquarium fill if possible, and also for evaporation top-ups and routine seawater change mixes.

The marine system should not be overstocked. Proper stocking allows for high water quality which by definition is lacking in nitrate (see article ‘Stocking The Salt Water Aquarium Part 1‘ and also Part 2 under the sub-heading ‘The Basics‘).

How does the type of filtration help?

If the aquarist is using live rock of sufficient quality and in sufficient quantity, this excellent filtration can deal with nitrate as it completes the full nitrogen cycle, the nitrate being released from the aquarium after conversion to a gas. This is ideal, of course, but the aquarist must be sure not to overload the filtration with fish.

If another bio-filtration type is in use, for example canister filters or trickle filters, then once the nitrogen cycle has reached the production of nitrate stage that is as far as it goes. Seawater routine changes and/or other methods of nitrate control are required. If the nitrate level is persistent, and is not reducing, or is even rising despite seawater changes, then there are methods to reduce it. One good introduction is to construct a DSB (deep sand bed) if possible (see the articles ‘Deep Sand Bed Construction‘ and ‘Deep Sand Beds‘ both under the sub-heading ’Filtration’).

Some aquarists who have a sump, or even utilise the display aquarium, use algae to assist in combating nitrate (and phosphate). This is the macro-algae Caulerpa (see the text ‘Caulerpa‘ – this is not under Articles, but can be found by going to the right side of the page and looking under ‘Categories’. Go down to the bottom of the list to ‘Problems’, and click on ‘Algae’, which is at the very bottom).

One point I will make here which is a repeat of what is stated elsewhere is to do with feeding. This is one of the major ways, probably the major way, that nitrate (and phosphate) get into the aquarium.

Overfeeding! Until experience has been obtained and the aquarist knows how much should be fed, it is very easy indeed to overfeed. It is often done because of anxiety as to whether the fish etc are getting sufficient to eat. Fish are very good at ‘begging.‘ The fish will often eat until they can eat no more – this is because they instinctively eat while there is food available. They do not know, as in the wild, when further food will be available. Unfortunately, when food is taken in to such an extent some can be excreted half digested which adds to the likelihood of nitrate. In addition, the aquarist can place too much food in the aquarium anyway, and the excess not taken by the fish sinks and generally rots. This leads to nitrate. It also follows that if the aquarium is overstocked then feeding is going to be excessive, and coupled with a newcomer’s inexperience which permits overfeeding anyway there is going to be even more nitrate. Digressing – in a newly set-up system this overfeeding can also put a potentially dangerous strain on the bio-filtration. (For feeding, see the article ‘Feeding Time!‘ under the sub-heading ‘Care and Maintenance’).

When it is considered that one gram (about a teaspoonful) of flake food with a protein content of 50% can convert to 336ppm (parts per million) of nitrate* then overfeeding causing a problem can be understood.

I hope that this text along with the articles noted will help to bring together the causes of, and methods of dealing with, nitrate.

(* Reference: Helmet Debelius & Hans A Bach. Marine Atlas)

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