Reef Central Online Community - Ozone and Nitrates

I do not think that ozone will be the best way to go about reducing nitrate if it is elevated. The number 9 listed in my article is what folks claim about it, not necessarily what it does.

I discuss why some may observe a real effect below:

Ozone and the Reef Aquarium, Part 1: Chemistry and Biochemistry
http://reefkeeping.com/issues/2006-03/rhf/index.php

Ozone and the Reef Aquarium, Part 2: Equipment and Safety
http://reefkeeping.com/issues/2006-04/rhf/index.php

Ozone and the Reef Aquarium, Part 3: Changes in a Reef Aquarium upon Initiating Ozone
http://reefkeeping.com/issues/2006-05/rhf/index.php

from the first one:

"Oxidation of Organics by Ozone: Skimming and Nutrients

Another result of breaking some organics into smaller, more hydrophilic bits (Figure 3 and 4) is that it often increases their bacterial biodegradability.27-29 Therefore, the ozone may need only to start the degradation process, and bacteria in the aquarium can finish off the organics by uptake and metabolism. Large humic acid molecules, for example, are converted by ozonation into smaller fragments that are more readily taken up and metabolized.29 This process may, in fact, be why some aquarists report drops in nutrient levels after initiating ozone. It is not because ozone directly impacts either nitrate or phosphate (it does not react directly with either), but the newly bioavailable organics may drive bacterial growth, just as adding ethanol (e.g., vodka) or sugar might. The growing bacteria need nitrogen and phosphate, and if they satisfy those needs by taking up nitrate and phosphate, the levels of those nutrients in the water may drop. That effect, however, may be only temporary as the initial burst of new bioavailable organics winds down, and a new stable state is reached with lower levels of organic material and similar levels of inorganic nutrients.

Skimming is a complex process that has many subtleties. The previous sections have discussed how ozonation modifies organic molecules , and we can then extrapolate how those processes impact skimming. Years ago it was widely claimed that ozone use increased skimming, and I claimed then that I didn't see how that could happen directly. Most organic compounds likely to be found in significant quantities in a reef aquarium will become more polar and likely less skimmable after it reacts with ozone. Figure 3, for example, shows how oleic acid (readily skimmed) gets converted into more polar compounds that will not be so readily skimmed as they will not be as strongly attracted to an air water interface.

A small portion of organic molecules in reef aquarium water may become more skimmable if, for example, they become more hydrophobic after reaction with ozone. They may also become more skimmable if they were totally hydrophobic before ozone and were transformed into molecules with polar and nonpolar parts (called amphiphilic) which more readily absorb onto an air water interface and are skimmed out.

Are there other ways that skimming might be increased besides these two processes? I hypothesized in a previous article that it was due to the growth of bacteria (either in the water itself, or bound to surfaces), and possibly also the release of new organic molecules as they grew, that caused the effects some aquarists observed.

It seems as if the tide of opinion has turned, however, and most aquarists now claim that the amount of skimmate is reduced significantly when using ozone. Many claim that the collection of skimmate has nearly stopped in their aquaria when starting ozone. Why the difference compared to past opinion? That's hard to say, and may depend on the types and qualities of the skimmers available now compared to years ago, as well as changes in other husbandry practices. In any case, the overriding experience of many aquarists today is that skimming is reduced, and the presumed reason is that the organics are being made chemically less skimmable by ozone. The remaining organics would then be removed more by bacterial processes than before the initiation of ozone in the same aquarium. "