Ah okay so free floating parasites that enter the skimmer wont be killed by the ozone?
Not typically, no. I address that here:
Ozone and the Reef Aquarium, Part 1: Chemistry and Biochemistry by Randy Holmes-Farley - Reefkeeping.com
Ozone and the Reef Aquarium, Part 2: Equipment and Safety by Randy Holmes-Farley - Reefkeeping.com
Ozone and the Reef Aquarium, Part 3: Changes in a Reef Aquarium upon Initiating Ozone by Randy Holmes-Farley - Reefkeeping.com
From the first one:
Reducing Bacteria When Using Ozone
Bacteria and other organisms suspended in water can be killed by adequate exposure to ozone. That process is widely used to disinfect drinking water and wastewater in a variety of applications. The doses and exposures of ozone required for disinfection, however, are quite high. They are higher than are used in reef aquarium applications, where typical doses of ozone range up to about 0.3 ppm in typical contact chambers, and last for only a few seconds. Consequently, aquarists must be careful when translating disinfection literature to reef aquarium effects.
In a recent study of a recirculating seawater system,35 the dosing of 0.52 ppm of ozone was tested for its ability to decrease the system's bacterial load. That dose is similar to a 300 mg/hr ozone unit applied to a typical small skimmer flow rate of 150 gallons per hour (568 L/h). In this experiment, the levels of suspended bacteria (both
Vibrio and coliform) were analyzed in a variety of locations (intake, pre-ozone, post-ozone, pre-tank, and post-tank). In no case was there a statistically significant reduction in bacteria. Even the addition of a venturi injector to the contact chamber did not adequately help (although it trended toward fewer bacteria, the result was not statistically significant). For comparison purposes, at higher ozone concentrations and contact times (5.3 ppm ozone for 240 minutes),
Vibrio vulnificus is easily killed, with fewer than one in a hundred million of the initial bacteria remaining.36
How much ozone, and for how long, is required to kill suspended organisms in seawater? In one study of a suspended dinoflagellate algae (
Amphidinium sp. isolated from Australia's Great Barrier Reef), it was found that 5-11 ppm ozone for six hours of exposure was required to kill 99.99% of the organisms.37 While that kill rate is impressive, that exposure is far higher than is ever achieved in a reef aquarium application. Lower doses and shorter contact times had smaller effects. A dose of 2 ppm and a short contact time (with the time not stated in the paper) showed a reduction in bacteria of abut 98% (which is still quite significant, but would not be referred to as disinfection).
Similar results were found for the spores of the bacterium
Bacillus subtilis.38 In this case, doses of 14 ppm ozone for 24 hours were required to kill 99.99 percent of the spores. In another study 99.9% of fecal coliforms, fecal streptococci and total coliforms were killed with 10 ppm ozone and a contact time of 10 minutes.39 The exposure of
Vibrio species and
Fusarium solani (bacteria that are pathogenic to shrimp) to 3 ppm ozone for five minutes killed 99.9% of the bacteria.40Water from a seawater swimming pool was effectively sterilized using 0.5-1.0 ppm ozone in a contact tower.41
The data for the disinfection of freshwater systems are much more extensive, and so include more data at lower contact times and concentrations. In one experiment at a Rainbow trout hatchery, the addition of 1-1.3 ppm of ozone with a contact time of 35 seconds reduced heterotrophic bacteria in the aquarium water itself by about 40-90%.42
Does the ozone used in a typical reef aquarium application reduce bacteria? Maybe, but certainly not to the extent required for disinfection. Still, a reduction of 50% of the living bacteria could have significant effects. The above study in the trout hatchery showed that the use of ozone at several times the typical reef aquarium rate and for about five to ten times the typical contact time results in such a drop. While the data are unavailable, I expect that the bacteria in the water exiting a normal reef aquarium's ozone application are not decreased by as much as 50%.
It seem reasonable to conclude from such literature studies that most bacteria that enter the ozone reaction chamber in a typical reef aquarium application will not be killed by ozone or its byproducts. If killing bacteria in the water column is a goal, then a UV (ultraviolet) sterilizer may be more useful.
Reducing Other Pathogens When Using Ozone
There has been extensive analysis of the amount of ozone needed to kill the human pathogen
Cryptosporidia parvum in freshwater. Most such studies are looking for significant disinfection, but some data points show the effects at lower doses and contact times, and some researchers have developed models that suggest the amount of killing at any dose/time combination.43 For example, at 22° C approximately 63% of the organisms would be expected to be killed at 1 ppm ozone with a contact time of one minute. The contact times and concentrations are inversely related, so at a contact time of six seconds, the required dose to kill 63% is on the order of 10 ppm ozone. At 0.3 ppm ozone and a six second contact time, typical for the high end of reef ozone applications, less than 5% of the organisms would be expected to be killed.
Many viruses are much easier to inactivate with ozone than are other pathogens.44 Enteric adenovirus, for example, is inactivated to the extent of 99.8% after exposure to 0.5 ppm for 15 seconds.44 Feline calicivirus is inactivated to the extent of 98.6% after exposure to 0.06 ppm for 15 seconds.44Poliovirus type 1 was inactivated to 99% within 30 seconds of contact time at 0.15 ppm ozone.45 Hepatitis A virus was inactivated to the extent of 99.999% within one minute at 1 ppm ozone.46 Norwalk virus was inactivated by 99.9% in 10 seconds of contact at 0.37 ppm ozone.47 Adenovirus type 2 was inactivated by 99.99% by 0.2 ppm ozone with a contact time of about one minute.48
The eggs of a pathogenic helminth (
Ascaris suum) were killed to the extent of 90% by exposure to 3.5-4.7 ppm ozone for one hour. One additional hour of exposure killed the remainder.49
It seems reasonable to conclude from such literature studies that many viruses that enter the ozone reaction chamber in a typical reef aquarium application may be killed by ozone or its byproducts. Larger pathogens, however, are likely much more resistant to ozone, and are unlikely to be killed. For such ends, a UV sterilizer may be more useful, but still may not be completely effective.
