Ozone (O3) was once a popular staple in the 1990s and over the past two to three months I have begin having more discussions on its use and hearing more aquarists applying them to their reefs. I believe there will always be a group of Ozone lovers, and rightfully so; its ability to degrade organics [...]
Ozone (O3) was once a popular staple in the 1990s and over the past two to three months I have begin having more discussions on its use and hearing more aquarists applying them to their reefs. I believe there will always be a group of Ozone lovers, and rightfully so; its ability to degrade organics and increase water clarity are unrivaled. [Public aquariums are prime example of ozone lovers, and generally use the oxidizing filtration]. So why has Ozone in fallen out of favor in the past? I largely attribute it to the shift towards “natural approaches”. As refugiums garnered attention there appeared to be a negative correlation to ozone among the everyday marine aquarist. This also held true with the rise of bacteria based systems such as Zeovit. Korallen Zucht and manufacturers of similar products state that Ozone and UV are not to be used in conjunction with their filtration methods.
Ozone is a powerful oxidizer consisting of 3 oxygen atoms
I’m not advocating that aquarists should not follow instructions, per se, but the bacteria killing abilities of Ozone are often overstated and I believe this realization is linked to the general re-interest in Ozone over the past 2-3 years, including the recent surge in ozone interest among my own reefing circles. One of the most often cited studies on this matters is from 2002, Microbial analysis of ozone disinfection in a recirculating seawater system.
I must give credit to Dr. Randy Holmes Farley for putting this piece out into the online reefing world, in his RK article Reefing and Ozone he summarizes the study well. Emphasis placed my own:
…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).
Everyone’s ozone application will vary as will the effectiveness, particularly when used in a skimmer. Skimmers are by far the most popular method of employing O3. However, skimmers are not designed to optimize ozone. I must again default to Dr. Holmes’ prior work which lays out 3 reasons why skimmers are not the ideal ozone reactor, and which I agree:
1. Their water and air flow rates, and even their engineering design itself, are optimized for skimming, not for ozone injection and reaction. The longer the ozonated water has to react, the more oxidation of organic molecules can take place. This is not a design criterion with skimmers, where the air/water contact time is maximized, but the water alone is not held for any purpose. If the water’s flow rate is too high, and hence its turnover rate too high, the concentration of ozone in the water, and the contact time for it to react with organic materials, may be less than optimal.
2. Both the air and water exiting the skimmer should optimally be passed over activated carbon to reduce the highly oxidizing and toxic species being sent into the aquarium and into the aquarists’ home air. Many skimmers are not set up to efficiently pass the air over carbon, and high water flow rates can make it difficult to achieve adequate contact with activated carbon.
3. Many skimmers are not designed using materials suitable for prolonged ozone exposure.
With the recent trend towards shorter, higher air flow skimmers we’re seeing a drastic reduction in ozone contact time, making modern skimmers even less ozone friendly. Dedicated Ozone reactors have been available on the market, some good (e.g. MTC Pro 240D) some not so good (Coralife). Recently we’re seeing more dedicated ozone reactors being made and more interest in them.
Ozone reactors provide slower flow through rates, dedicated reaction chambers, and easier post-ozone carbon filtration to eliminate that ozone smell and related byproducts. Unless a carbon lid is placed on top of the skimmer, or a downdraft style waste collector is used with a carbon filter attachment, skimmers will release ozone into the surrounding air. Generally this will cause no harm, but the smell of ozone may not be the ‘home scent’ you’re looking for. Ozone also innevitably wears on skimmers. Rubber o-rings used in the skimmer neck are prone to degradation.
Schuran’s Ozone Module XL incorporates a shower style reaction chamber. Note the carbon to the right.
This Siam Ocean Ozone reactor incorporates a plastic media to increase the water’s contact time.
If you’re considering using ozone, you may want to look at dedicated Ozone Reactors. New designs from Schuran, Siam Ocean, and other manufacturers look promising, as do many of the DIY plans available online.