Question:
A number of people have reef tanks without a "technical" denitratorand they don't do water exchanges. I'll reserve opinion until laterabout whether or not that is a good idea.

Your question can be recast in the following ways:

- Do I need a denitrator on my reef aquarium?

- How well do the various denitrators on the market work?

- Will a denitrator alleviate the need to do partial water exchanges on my aquarium?

Answer: The answers are... first, there isn't any formal requirement fora technical denitrator on a reef aquarium. It is possible tomaintain "natural" systems that have negligable nitrate buildup.Indeed, one can fairly say that if nitrate is accumulating ina reef aquarium, you are pushing the "natural" component of the systempast its limits. And I should define what I mean by natural inthis context. In this context I mean the anoxic compartments that occurin both the live rock and substrate in reef systems. Whether or not"natural" systems are very natural is another subject.

Many people will tend to push a reef system past its "natural" carryingcapacity. The most common way to do this is to add a fairly largepopulation of fish to the system. The fish generally need to be fed,and that means that the system needs to be able to process and eitherabsorb or export the nutrients in the food. Nitrogen is only one suchnutrient. It is the most widely discussed and arguably one of themore easily testable nutrients. The inorganic forms are easily testable,and with some minor exceptions, they are fairly soluble in the system,so they won't "hide" the way that phosphorus and iron can.

Since fish are the most commonly "fed" organisms in reef systems, thisproblem is usually illustrated based on fish. There are of course otherorganisms in reef aquariums that may benefit from feeding, and feedingthem presents similar issues.

Usually if a person thinks or has reason to believe that a denitratoris required for their system, they generically need a nutrientexport mechanism.

The best documented examples of denitrators are those used by publicaquaria to deal with nitrate accumulation in their systems. Thesesystems definitely work. Public aquaria often have a secondarymotivation for running denitrators. They typically use ozone in theirsystems, and ozone forms persistent toxic products when bromide ispresent in the seawater mix. Denitrating filters reduce the steadystate concentrations of these oxidized toxic products in their systems.

Do you absolutely need a denitrator? No. But if you plan to havea substantial fish population, you do need an export mechanism fornutrients. The most commonly employed systems are foam fractionationand algal turf scrubbers.

With regards to question number two, whether or not commercial denitratorsactually work, I don't know since I have not used them. I would re-emphasizethat they are not a complete nutrient solution in any case, since theydeal only with nitrogenous waste products. There is little doubt that onecan construct anoxic dissimilatory denitrifying filters that do work,since they are documented to have worked in the well-studied context ofpublic aquaria. I have some reservations about the electrochemicaldenitrators on the market. Not about their theoretical efffectiveness,but rather about their logenvity and ability to play nicely with allother components of a functioning reef system.

The final question is whether or not having a denitrifying filter willmean that you need to do fewer water exchanges on your system. Perhaps.However, there are many other reasons why partial water exchanges arebeneficial. Marine salts now do a reasonably good job of recreatingthe major and minor components of natural seawater (with someexceptions.) They are inexpensive and widely available. Water purificationtechnology has also advanced substantially, so being concerned aboutadding bad stuff to your system when paritials are done isn't nearly theissue now that it was in the beginning of the marine hobby, when someof the pioneers had salts custom compounded for them, at substantialexpense. Partial water exchanges are a very powerful, broad spectrumtechnique for assuring that your system doesn't drift too far away fromnatural seawater ionic ratios. For examples of how powerful they canbe, you can look at some simulations that I did of this process in theback issues of Aquarium Frontiers. The best part of this is that itisn't necessary to test for individual components. You just need tofind a quality salt mix and do the partials, and the system isnaturally clamped near natural seawater ionic ratios.