Exactly. But I use mine without as I noticed little difference.
I discuss the reasons for it here:
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 second one:
http://reefkeeping.com/issues/2006-04/rhf/index.php#3
Air Drying
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Ozone generators using corona discharge operate most efficiently when the air entering them is dry. While the exact relationship between humidity and the ozone production rate depends on the generator's design, most commercial ozone generator manufacturers (O3ozone, Ozone Solutions and Lenntech, for example) show graphs of ozone production vs. humidity that look something like Figure 3. Many aquarists know the rule of thumb that ozone generation efficiency drops by about a factor of two between dried and undried air, and Sander makes a similar claim for its ozone generators on its website. Specifically, Sander claims that drying the ambient air with a relative humidity of 50% to dry air with a dewpoint of -40°C causes a 50% reduction in the ozone output of one of its line of ozone generators.
Data such as that in Figure 3 would seem to show that the maximum potential effect of drying is likely to be somewhat larger than two-fold if using ambient air, which can have dewpoints running up to 20°C or even higher, compared to very dry air (with a dewpoint below -60°C). For convenience in interpreting Figure 3, the table below shows the relationship between relative humidity and dewpoint when the air temperature is 70°F (21.1°C). Obviously, the air must be very dry to have a dewpoint below -20°C. It is not obvious, however, whether the sorts of air dryers used by hobbyists approach or exceed this low dewpoint.
It is also claimed that higher humidity in the incoming air can increase the output of nitric acid, but not all researchers agree on this assertion.2 Some resources3 recommend that the dewpoint be kept very low (~-60°C) in order to prevent corrosion of the unit itself by nitric acid's formation inside it. Again, however, it is not obvious whether the sorts of dryers used by hobbyists approach this very low dewpoint.
Figure 3. The relationship between the dewpoint (humidity) and the relative amount of ozone produced in a typical corona discharge ozone generator.
One aquarist reported corals in his aquarium started looking poorly, and discovered that there was a blue liquid in the tubing between his ozone generator and a brass fitting. he had not been using an air dryer, and it was a humid day. That liquid may well have been nitric acid in water that corroded the brass fitting to release copper, that then made its way to the aquarium. A more extensive discussion of the chemistry behind nitric acid formation is presented in the next section.
In any case, most ozone generator manufacturers suggest that the air be dried before it enters the generator, and aquarists have several options for drying the air. Some commercial devices can dry air rapidly and automatically, although they are considerably more expensive than other options. These commercial devices are especially useful in high air flow applications (many liters per minute).
The simplest dryer is a plastic tube filled with a material that binds to moisture in the air. The air flows in one end and out the other, and gets dried while passing through. Red Sea sells such a device in at least two sizes. Their material (silica gel) changes color from blue to pink as it is exhausted, and it can be regenerated in a standard oven by warming it up, thereby driving off the absorbed water. Unfortunately, my device came missing a critical O-ring, and when I resorted to making it myself, the unit sometimes could not hold adequate pressure. It also seemed to become depleted faster than I had hoped. In my system I used the larger size (500 g), but found that it typically became depleted in two weeks or so. That result is apparently mirrored by others' experiences, so anticipate such a discharge period. Nevertheless, the color changing ability makes depletion apparent. I also found a surprisingly small effect of using the dryer on ozone in the effluent from the reaction chamber, and on overall aquarium ORP. Details of that finding will be discussed next month, but that result may reflect a lack of effectiveness of the drying tube, or alternatively, a lack of a large effect of humidity on the ozone production by the Aquamedic ozone generator that I used.
Some aquarists use two units in series, so one can be swapped out for regeneration while the other is still in place. Figure 4 shows the setup used by Jose Dieck, in which he has drying tubes mounted on a wall with quick disconnects to permit rapid swapping in and out as necessary. In addition to simplifying the replacement process, such a setup may drive the dewpoint lower than a single pass system using the same tubes.
Figure 4. The ozone generation setup used by Jose Dieck, showing two drying tubes used in series.
Do-it-yourselfers may be able to buy silica gel themselves and fashion a drying tube. Other materials might work, but may entail complications. Damp-Rid, for example, may actually liquefy in the presence of too much moisture, and it may also not reduce the humidity enough.
