Ionizers don't change anything to a plant's growth. In too large amounts and over time, it can be toxic to humans too ... but many will question this.

Actually, I made a mistake. Ozonators can be dangerous for humans. I don't think ionizers can be harmful.

Ozone is not harmfull as long as you dont look into the light as this will more than certainly cause blindness, ozone can harm the plant if used incorrectly as it can burn the leaves.

Ionizers send negative ions into the air which apparently cling on to the particles in the air which is supposed to clean the smell, but it can mean that the buds dont smell.

Ozone CAN create some respiratory damage.
I'll see if i can find an article on the subject.

But anyway, I've always prefered the good ol' can filter.

As for ionizers, they release negative ions which react with particles in the air and make them drop to the floor. If your buds were small enough to react with a (-)ion, then it won't smell. But i'd be very surprised to imagine a bud grown around a ionizer would loose it's smell.

With an ionizer, your grow room air will smell fresh, much like after an electric storm

Dangers of ozone in your grow:
BBC NEWS | Health | Simple test for ozone lung damage
The Lung Association: Ontario: Research Report: Ozone and Human Health
Having shown that ozone can be very bad for your lungs, you still can use ozonators. Only you can't over-do it. But franckly, there are more effective ways to elliminate the odor and ozone can be smelly too.

I go to this guy's house and I know he's got a grow in there because the place reaks of ozone in the backyard when we sit at the patio.
The smell isn't as strong as weed of course but it is there.

Stay away from ozone, it can be dangerous, it is a polluant and it doesn't smell good. A good old fashion can filter will do you perfectly.
Even if you have a sealed room, you still need to move that air around, right? Well, while you are moving that air around, might as well pass it through a filter while you're at it ... right?

I use an ionizer in the rest of the house because it makes the air feel fresh and crisp but I think you'd need too many of them in a grow to make them worthwhile.

Ozone Fact Sheet - American Lung Association site
Ozone Fact Sheet

Ozone (O3) is a highly reactive gas that is a form of oxygen. It results primarily from the action of sunlight on hydrocarbon vapors and nitrogen oxides emitted in fuel combustion.1 Ozone reacts chemically (“oxidizes”) with internal body tissues that it comes in contact with, such as those in the lung. It also reacts with other materials such as rubber compounds, breaking them down.

• Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. Ozone exposure may lead to:
  • premature death2
  • shortness of breath
  • chest pain when inhaling deeply
  • wheezing and coughing3
• Long-term, repeated exposure to high levels of ozone may also lead to reductions in lung function, inflammation of the lung lining and increased respiratory discomfort.4
• Exposure to elevated levels of ozone greatly increases the risk of asthma attacks, need for medical treatment and for hospitalization in persons with asthma.5
• The U.S. Environmental Protection Agency (EPA) estimates one out of every three people in the United States is at a higher risk of experiencing problems from ground-level ozone.6 Five groups of people are at particular risk:
  • people with pre-existing respiratory disease; those already afflicted with lung disease such as asthma, chronic bronchitis and emphysema7
  • senior citizens8
  • people who work or exercise outdoors9
  • children, because their airways are smaller, their respiratory defenses are not fully formed, and their higher breathing rates increase their exposure10
  • “responders”—otherwise healthy individuals who experience health effects at lower levels of exposure than the average person.
• Ozone levels typically rise between May and October when higher temperatures, an increased amount of sunlight, and stagnant atmospheric conditions promote transformation of air pollutants into ozone.
• For almost two decades prior to 1997, the federal air quality standard for ozone had been 0.12 parts per million (ppm) averaged over one hour, but tests carried out on healthy adults and children undergoing moderate exercise while exposed to lower levels of ozone showed a decrease in subjects’ breathing ability.11
• In response to a lawsuit filed by the American Lung Association, the U.S. Environmental Protection Agency in July 1997 set a more protective ozone standard of 0.08 ppm averaged over an eight-hour period. Compliance is based on the fourth highest reading per year averaged over three years.12
• The national ozone standard is under review currently, the result of yet another American Lung Association legal action. EPA had not formally reviewed scientific research on ozone since 1996, although the Clean Air Act requires such reviews every five years. The American Lung Association took legal action in December 2002, to require the Agency to schedule a formal review. In a settlement, EPA agreed to complete that review by December 2007.
• To reduce ozone air pollution, the American Lung Association supports stringent controls on motor vehicles and commercial and industrial sources of the hydrocarbon compounds and nitrogen oxide emissions. These controls include:
  • stricter pollution control requirements for power plants, including those that will bring older power plants up to current emissions standards
  • stronger pollution control requirements for new motor vehicles and small engines
  • cleaner fuel standards, including diesel
  • cleaner diesel vehicles, especially heavy equipment and other diesel engines
  • improved in-use performance of existing pollution control equipment
• The ground-level ozone in the lower atmosphere (troposphere) should not be confused with the natural protective layer of ozone in the upper atmosphere (stratosphere). Although both are made of the same molecules (ozone), the ozone in the upper atmosphere protects us from the sun’s harmful ultraviolet rays, while the ozone in the lower atmosphere harms us.

For more information, call the American Lung Association at 1-800-LUNG-USA (1-800-586-4872), or visit our web site at http://www.lungusa.org.

edit: an other characteristic of ozne is that it kills bacteria in your grow room. It might sound good but it won't kill just the harmful bacteria, it will kill the beneficial bacteria as well.

what about recycling the air
i.e pumping the air throug 10' - 20' of duckting coiled up in a fridge or an air conditioned room and then back into your grow room
....of cource thats for a smaller grow room

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ive heard to use co2 mostly during flowering, im a rookie so i hope thats right

Ventilation is an old schoolethod of maintaining the temperature of the romm at levels low enough to have the palny ts CO2 needs met by the 300 to 400 ppm found in typical air. While this is fine as long as the lighting is not at a high PAR it is inadequate for ya HID lighting at 50 to 70 plus watts per square foot which is becoming the norm for fast grows such as SOG's etc. If the lighting is as mentioned then CO2 is lacking even with constant ventialtion therefore you are just wasting a large portion of the light your providing.

Now consider CO2. To best utilize CO2 a closed sytem is most efficient. Using CO2 and using a closed room will cause excessive humidity, therefore an airconditioner can dehumidify while it is keeping the room th emperature below 90 degrees. I repeat an air conditioner dehumidifies. Some might be alarmed by this but cosnsider with high temps and plentiful CO2 , plentiful nutrients and water a plants will transpire very heavily if the humidity is kept at around 40%. All these things together mean very fast growth as tranpiration is how plants take up nutrients and high lighting and CO2 means lots of photosytheis. Put these things together in one room at the same time and you have very, very fast growth. However it is not a forgiving system as it is like a sytem on methamphetamine. If you remove one of those needs, such as dehumifictaion or heat control or water the plants can fry in one day easily. About the only thing that is tolerable in such a sytem is if the lights go out.

The reason some people st ay a DWC needs more ventilation can be because if the lighting is also good a shortage of CO2 will become apparent and the humidity will also become excessive do to all the evaporating water experienced by many DWC systems. If the humidity is excessive then transpiration slows or neraly srtops entirely. No transpiration or respiration no growth.

In a closed system to control the odor that can happen when the door is open you only need to use a small carbon can or some such carbon filtration in the closed room. You should never have a need to ventilate a closed (sealed) room grow. As for the airconditioning. If you use air cooled tubes on your lights you might find the airconditioner will not need to run too much. If this the case you might actually need a dehumidifier. However, it is usually never necessary to have a humidifier in a sealed grow unless your growing in a very hot area where the air conditioner runs almost constantly. A 12000 btu air conditioner can easily remove 60 to 70 pints of water per day. I find the easiest grow room to maintain is a sealed system with very heavy insulation. My grow rooms are surrounded with 5.5 inches of foam insulation and the doors are foam core insulated and weather stripped. I have reef aquriums so I use water cooled lights. HID lighting is 85% wavelengths that produce heat. So for ever 1000 watts of lighting that goes into the room approximattely 850 watts need to be removed. Good water chiilers are more efficient than good air conditoners.

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