This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Feb 23, 2005
Reaction score
hey guys,,,,,a few ???? first is co2 worth the problem......if so what do i need ,,,,and about what should it cost me to get started ,,,thanks in advance
I found this online and posted it in another thread on CO2....maybe it will help you....

Found this online....take from it what you will.

A good grow room will have good temperature and humidity control with different settings for day and night and a gradual change over between. Night temperatures should normally be about 5oC below day temperatures whereas night humidity should be well below that of day time (perhaps around 50%). An exception to the 5oC night drop may be for short periods when you are trying to reduce spindly growth. Good interaction between CO2 enrichment and ventilation is vital to ensure that no precious CO2 is wasted. The system must be easy to use and provide simple data logging to show you what the temperature, humidity, CO2 and light levels have been doing while you weren’t there.

Good fail safes are essential. What happens if the air-con fails, what if the dehumidifier fails? or if the power fails when the lights are on? (when power resumes we need to bring the lights back on methodically, taking into account minimum cooling periods and time delays between banks switching on in order to avoid power surges). An alarm system that will text or phone you if something goes wrong or if an intruder is detected. All of these things come to mind.

If you are looking for ultimate growth then CO2 injection must be considered but it does bring with it a further difficulty. When injecting CO2 you need to keep the growing area closed with fans off. If using ordinary lights the temperature will quickly rise and soon you will need to switch on fans to cool the room down. This limits the time that you are able to inject CO2 and it also increases CO2 wastage (although a good controller will minimise this by stopping CO2 injection well before venting is required).

Hint 1. Use air cooled lights if you intend using CO2 enrichment. This allows longer periods of injection before venting is required.

Even so, the crop under lights and with CO2 enrichment will be growing vigorously and will transpire heavily. This will raise the humidity and again it will become necessary to turn on the fans to reduce this. A better option is to use a dehumidifier to keep the humidity at an acceptable level without the need for frequent ventilation.

Remember also, that the desired humidity varies depending on the stage of growth starting from a very high level for cuttings/seedlings and reducing considerably when flowering. Good controllers now offer automatic scheduling of all important growroom variables, changing these automatically as the crop grows.

Hint 2. Use a dehumidifier to extend the CO2 injection period to the maximum possible.

If you have decided to use CO2 then be aware that the rate of injection must match the growth stage of the crop. For example, if you inject high levels of CO2 at the cutting stage, the roots will not be able to cope with the attempted growth rate and the cuttings may be damaged.

Hint 3. Start with CO2 of 600ppm and increase it gradually as the plants develop. You should be able to increase by about 100ppm every four days days until you reach your target CO2 level for the mature crop. This is typically 1100 to 1500ppm.

Now we’re really cooking with gas! Growth rates will be high and we need to ensure that the crop gets adequate lighting for high growth. With two banks of lights you have an ideal situation. During vegetative stage of growth you require a lower intensity of light but for a longer period (say one bank of lights for 18 hours per day). During this period the controller should be set so that only one bank of lights is used at a time and the two banks are switched on alternately each day. This ensures that the crop receives light on both sides. During flowing, more light is required for a shorter period (eg 12 Hours) and for this stage both banks of light will be used. Modern controllers can be scheduled to do all of the above automatically. It will even switch banks if the light sensor detects low light (such as for a bulb failure) and will recover lighting correctly after a power failure ensuring that cool down periods are observed. When both banks of lights are programmed to be on together the controller will enforce a minimum gap between each bank switching on to allow the power surge from the first to die down before the second starts.

Hint 4. Use two banks of lights and program them to alternate during vegetative phase and for both to be on together during flowing stage.

In warmer climates or to ensure growing is possible during the warmer months of summer, an air conditioner may be used to keep the room cool and thus allow long CO2 injection periods. One disadvantage is that air-con tends to dry the air and to correct this some form of humidification is required.

Low humidity will also be a problem when regular lights are used (ie not air cooled) as the fans will be on most of the time and the combination of heating (from the lights) and fan ventilation is very drying.

Humidification can be achieved by using either a humidifier or a fogging nozzle. These both need a slightly different control as the humidifier can normally be switched on when the humidity is low and switched off when it is high. Fogging, on the other hand, tends to be more effective and needs to be pulsed on for short bursts to avoid putting too much water into the air. Fogging is the lower cost option if mains water pressure is available together with low pressure fogging nozzles. Ensure the nozzles are classified as foggers rather than misters. Droplet size should be below 80microns.

Of-course, your climate controller must have the intelligence not to humidify the grow room just before the lights turn off as leaving the crop damp and cool will lead to fungal disease problems.

Hint 5. If an air-conditioner or regular lights (non cooled) are used then humidification will be required. Use either a humidifier unit or pulsed fogging nozzles. The finer the droplet size the better.

Humidity must be carefully controlled especially during flowering as air filters become ineffective at high humidities.

Hint 6. Ensure that maximum humidity is programmed to be below 70% during flowering stage

Things do go wrong (bulbs fail, circuit breakers trip, CO2 runs out, intruders detected) and you need to know about these events as soon as possible. A good control system will have flexible alarms including dial out to a remote telephone or mobile phone.

Hint 7. Ensure that you have a good alarm system to warn you if anything should go wrong.

Lighting, CO2 and humidity all require frequent settings changes during the overall grow period. A good controller such as those made by Autogrow allow these changes to be pre-programmed so that you can’t forget to do them. Of-course, growth rates are never the same and so changes to the schedule must be easily made. With a telephone or internet link to your PC you can even make these changes remotely.
IME the CO2 was more trouble than it was worth, so I just went back to lots ans lots of fresh air.

Latest posts