Hydroponics FAQ

Welcome to the BGHydro Official Hydroponics FAQ section. Use the links or search box below to find your way around.

What are the benefits of adding CO2 to my grow room?

Many growers overlook the huge importance of CO2 to fast growing plants. CO2, along with light, are the two most important sources of food for plants. Plants take light and CO2, and through a process called photosynthesis, produce food for themselves. The nutrients that growers feed their plants are kind of like the salt and pepper, whereas the light and CO2 are like the meat and potatoes. The nutrients are necessary for photosynthesis to occur, but they are mainly a catalyst to allow the reactions to take place. In fact, if you were to analyze any plant, you would find that it consists of over 90 percent water, a few percent nutrients, and the rest is carbon.

Normal CO2 levels are between 300 to 500ppm (parts per million), depending on whether you live in an urban or rural area (we have almost 600ppm of CO2 here in Los Angeles!). Increasing these levels to 1500ppm can often have dramatic effects on your plants, including faster growth rates and increased yields. This is why it is so important to always have fresh air circulating into your grow room, or better yet, add supplemental CO2.

What are the most common ways of adding CO2?

The two most common devices used to produce CO2 are CO2 generators and bottled CO2.

Bottled CO2:

Bottled CO2 is perfect for small areas up to around 12' x 12' x 8'. CO2 tanks are available in several different sizes, but the two most common sizes used for enriching grow rooms are 20# and 50#. When full, a 50# tank weighs a considerable amount; even a very strong person will need a dolly to transport it. CO2 tanks can be filled at most welding and dry ice companies. Keep in mind before you bring your shiny new tank to a welding company that many of them will exchange your empty tank for a used full one rather than filling it up, so make sure to ask first. Most places will charge less than $20 to fill a 20# tank and $50 for a 50#. In addition to the CO2 tank, you will also need to purchase a CO2 Enrichment System to properly dispense the CO2. The enrichment system attaches directly to the CO2 tank with either a wrench or channel locks. Most enrichment systems consist of a pressure regulator and gauge, a solenoid valve, and a flow meter. The flow meter allows you to adjust the amount of CO2 coming out of the tank, and the solenoid valve allows you to attach a timer or other device to turn on and off the flow of CO2, thereby maintaining the desired level of CO2 (usually between 1500 and 2000ppm).

CO2 Generators:

CO2 Generators are generally a little more expensive than CO2 tanks and also produce a small amount of heat, but they offer several advantages. Generators operate on either propane or natural gas, both of which are less expensive and easier to come by than bottled CO2. Propane generators can operate using just about any propane tank, including the small ones used for barbeque grills. Some growers use the natural gas hookup provided for a gas dryer in their house to attach natural gas generator, which not only saves the labor of swapping out empty propane tanks, but also saves them money, as natural gas is much cheaper than propane. Some generators, such as the MegaGrowth, are vented so that you can attach an exhaust fan and eliminate some of the heat they produce.

Regardless of which solution you choose (bottled CO2 and an enrichment system or a CO2 generator), you will still need something to control it. Keep reading for information on how to accomplish this.

How do I control the amount of CO2 in my growing area?

There are several ways in which a grower can control the level of CO2 in the growing area, assuming of course that the growing area in enclosed. Unless you are using a digital CO2 monitor/controller or complete environmental controller, you will first need to determine how many cubic feet per hour (CFH) your CO2 device dispenses. If you are using a CO2 generator, the CFH is usually a fixed amount, e.g. a CD-3 CO2 Generator produces 3 CFH. However, if you are using a CO2 Enrichment System in conjunction with bottled CO2, then the output amount can be varied depending on the flow meter setting.

If you are using a C02 tank with an Enrichment System you will need to use the following formula in order to determine the proper C02 level and flow rate for your needs:

  1. Determine the size of the room in cubic feet (CF). This is done by multiplying the length by the width by the height of your room. If your room measures 10 long by 10 wide by 8 high, then your total CF is 10 x 10 x 8 = 800 CF.
  2. Determine what your desired level of C02 is and subtract the existing amount of C02 thats already present in your room. Most growers will prefer about 1500ppm (parts per million) of C02. Plants will respond to up to 2000ppm, but this amount is generally not used since plants will utilize such high levels only if every other aspect is in perfect balance (which is extremely difficult to achieve). In general, there is about 500ppm of CO2 already present in the atmosphere if you live in a big city, around 300 if youre in a less populated area. Assuming that there is 300ppm present where you live, you would have to add an additional 1200ppm in order to reach your target level of 1500ppm.
  3. Determine how many CF of CO2 you need to inject. Multiply the volume of your room by the amount of C02 necessary to raise the C02 ppm to the target level: 800 CF x .0012 = 0.96. We will round 0.96 up to 1. Therefore, in order to raise the ppm level in your room to 1500ppm, you will need to inject 1 CF.
  4. Determine the flow meter setting. Assuming that after 3 hours C02 levels will return to normal due to plant use as well as leakage, we will divide the 1 CF of C02 into three 1 hour increments. 1 CF divided by 3 = 1/3 CF or 0.333. Therefore, every hour an 800 CF room needs 1/3 CF of C02 in order to bring it back up to 1500ppm, and so your flow meter should be set to 0.333.

If you will be using a CO2 generator to supply CO2, refer to the following chart to choose the correct size. NOTE: This chart assumes that you will only have to raise the ppm in your room 1000ppm, not 1200ppm as in our previous example (multiply numbers by 1.2 to achieve values for 1200ppm).

The first row in the chart represents the total CF of your grow room.
The first column in the chart represents the cubic feet per hour that the generator puts out.
Each intersection will give you the amount of time needed to increase the ppm in your room by 1000. For example, a CD-18 generator will take about 4 minutes to increase the ppm by a 1000 in a 1200 cubic foot room.

NOTE: It is usually recommended that you choose a generator that is large enough so that it can fill your room within 10 minutes or less. If it takes more than 10 minutes for a particular generator to fill your room it is recommended that you choose the next size up.

If you will be using a CO2 generator that runs on propane, the following chart will be helpful:


This chart is used to figure out how long a tank of propane will last. This chart is fairly self explanatory. First, pick a generator from the left column, then follow it across to the propane tank size (in gallons) you have. The number that corresponds with the two selections will be the number of hours that you can operate the CO2 generator.

Now that you have decided which device you will use to supply the CO2 (CO2 tank + CO2 Enrichment System or a CO2 Generator), its time to choose the method in which you will control that device. Below are some common methods.

One Timer:

There are three types of timers which can be used: 15-Minute Increment Timer, Digital Timer and Repeat Cycle Timer (e.g. Cyclestat, IGS010, IGS011). Timers with increments of 30 or longer are less desirable, since we want to inject CO2 quickly and have more precise control. If you are not using an exhaust fan, you can get by with just one timer, otherwise you will need two; see below.

Two Timers:

If you are using an exhaust fan in conjunction with CO2, you will need to synchronize the two so that the fan doesnt come on at the same time as the CO2 and suck it out of the room before it has a chance to be used by the plants. Because of the precision required to this, you would need to use either digital timers or repeat cycle timers. In this situation, you would set the fan timer to come on long enough to vent the room completely, usually 15-30 minutes provided the fan has been sized properly. The CO2 timer would be set to come on right after the fan turns off. You would program the timers to repeat this cycle every hour during the light cycle.

CT-DH-3 w/ Repeat Cycle Timer:

In this scenario, you would first set the maximum desired temperature and humidity values on the CT-DH-3. Then plug your Repeat Cycle Timer (e.g. Cyclestat, IGS010, IGS011) into the left side and your exhaust fan into the right side. Now, if the grow room gets too hot or too humid, the left side (CO2) will shut off and the right side (exhaust fan) will turn on. As soon as the temperature and humidity levels fall back down, power will once again be restored to the left side and the cycle timer will once again cause your CO2 device to dispense CO2 for the proper length of time. If the temperature and humidity levels stay below the set points, then the cycle timer will just come on long enough to supply the proper amount of CO2, then shut off for the amount of time you have it programmed for, then turn back on again and so on. Refer to the illustration below. This scenario can also be accomplished using an Off-Switcher in conjunction with either an IGS020, 021, 030 or 040, depending on whether you want to take into account just temperature, just humidity, or both.


Digital CO2 Monitor/Controller:

Using a digital monitor/controller offers the most precise control by enabling you to set the desired CO2 ppm level and the controller will automatically turn on and off your CO2 equipment to maintain that level. The controller can also be plugged into a CT-DH-3, or an Off-Switcher can be used as in the previous example (just substitute the repeat cycle timer with the controller in the previous example) in order to synchronize your exhaust fan with the CO2 equipment. Some examples of CO2 monitor/controllers are the Green Air Products CDMC-6 and CDMC-7, and the Plug n Grow IGS061 and IGS100. The IGS100 also includes features similar to the CT-DH-3.

Complete Environmental Controller:

A complete environmental controller has the capability to control not only CO2, but also temperature, humidity, water pumps, lighting systems, etc. Some examples of these are the Plant Pro, IGS220 and MCC-1.

When and how often do I need to use CO2?

C02 should only be used when your lights are on, as plants only use CO2 during photosynthesis. C02 is most effective during the flowering stage, but BGH recommends using CO2 throughout the life of your plants for maximum results.

How do I keep my room from getting too hot?

Heat buildup in a grow room is a common problem among growers. We usually advise our customers not to go crazy and spend lots of money from the get go, but instead take it in stages. Start with the cheapest and simplest solutions first and graduate to more expensive and complicated one's if the problem persists. Proper planning of the grow room can make things a lot easier. Make sure that you have not only installed an adequate exhaust fan, but also make sure you have sufficient intake, otherwise your fan will not be able to do its job properly. In most cases, you will not need to use a fan for the intake, an adequate size opening in the room will do.

The next step towards cooling your room is to cool your lights. Most of the lighting systems and reflectors we carry have air-cooling options that allow you to hookup your exhaust fan directly to your reflector, eliminating the heat right at the source. Almost all air-cooled reflectors have to two vent openings. Many growers will simply attach their exhaust fan to one of the ducts with some duct hose so that the hot, stale air in the grow room will be sucked out along with the hot air in the reflector that is generated by the bulb. If you are using CO2, then you will want to suck air from an outside source, through the reflector, and back outside again so that you do not suck out any of the CO2-rich air from the grow room. This scenario also applies if you end up having to use an air conditioner, since you don't want to suck out the cool, air conditioned air. Most air conditioners have a vent which you will want to close so that it recirculates the air in the room instead of constantly sucking in air from the outside, especially if the air outside is hot.

If, after venting your room and installing an air conditioner, you still can't get rid of the heat problem, you may need to consider water-cooling your lights. See the lighting section for products such as the Hydro Coil Water-Cooling Jacket for more information on water-cooling.

What are the different methods of controlling odor?

BGH offers an assortment of different methods for controlling odors.

Odor Killer Spray and Gel

Odor Killer Spray and Gel is the simplest method of controlling odor. With the gel you simply remove the cap and leave it sitting in the room. In the case of the spray, simply spray into the air as necessary. After some time, the Odor Killer Gel will begin to evaporate. When the container is half full simply add some of the liquid refill to reactivate the gel. Although quite effective in small areas, Odor Killer products are usually not recommended for large areas.

MountainAir Carbon Filters

MountainAir Carbon Filters are the most effective choice for any grower who wishes to eliminate organic odors. The secret is in the carbon, which comes from a Pre Cambrian source making it the oldest and most effective carbon available. There are several brands of carbon filters on the market today, but almost all of them use coco coir carbon which doesnt filter as much of the odor and only lasts 8-12 months, and none can compare with the quality of the MountainAir carbon. Carbon filters can be used to clean outgoing air that is being vented out of a grow room or they can be used as a scrubber cleaning the air within the room.

The size of your Carbon Filter is determined by the Maximum Watts of Light that you are running in your room.

In order to determine the proper size filter you need, as well as the ideal fan size for that particular filter, please refer to this chart.

Ozone Generators

Ozone can be produced using a UV (ultraviolet) lamp or through corona discharge. Corona discharge units are typically more expensive, but they are capable of producing higher amounts of ozone, the output can usually be adjusted, are physically smaller, and dont use a lamp (which needs to be replaced every about 2 years).

Big Blue Ozone Generators

Big Blue Ozone Generators are available as either an inline generator or as a general purifier. The Inline models are used in conjunction with a fan and ducting. The fan pushes dirty air through the generator and then through some ducting and finally outside. The Big Blue Air Ball is a corona discharge unit that can be left in a grow area or room and plugged into the wall. When the unit is on it eliminates all odors in the room.

Air Lazer Ozone Generator

The Air Lazer Ozone Generator uses ultraviolet rays to react with the atmosphere and generate ozone. The ozone is then blown out from the unit and begins to eliminate odors within your room. The Air Lazer will cover up to a 10ft by 10ft room.

Air Maid

The Air Maid is a corona discharge unit that can be used to purify the air in your room. Available in two different sizes, this unit is the only programmable, fully adjustable ozone producer on the market.

How do I determine what size carbon filter and fan I need?

How do I connect my speed controller to my fan?

If you go to our website, you should be able to download the instructions for your particular speed controller directly from the item page itself. BGH carries more than one speed controller, so be sure to choose the correct model

What is the ideal temperature range for plants?

Air temperature within the grow room should be between 77 and 83 degrees Fahrenheit. Water temperature should be between 68 and 72 degrees Fahrenheit.

What is the difference between an Elicent and a Fantech Fan and why are centrifugal fans more expensive than Dayton or Suncourt fans even though they have less CFMs?

Elicent fans and Fantech fans are both considered inline centrifugal fans. The primary difference between centrifugal fans and other fans like squirrel-cage blowers (e.g. Dayton), axial fans, or Suncourt fans is the CFM power. Even though some blowers may have a higher CFM rating than some of the centrifugal fans, the static pressure that the centrifugal fans create adds the extra power that these other fans dont have. This static pressure is essential not only for venting lights but also for venting rooms. Once most other fans meet any type of resistance, like a reflector or a bend in the ducting, they will lose a significant amount of power. This loss in power will not occur with a centrifugal fan. Centrifugal fans are much more quite and energy efficient than other fans.

What size fan do I need to vent my room?

Due to the many variables that have to be considered, there is no exact answer or formula available to determine the fan size. But, we will at least try narrow things down as much as possible so that you can make an educated guess. The old rule of thumb is to try to replace the volume of air in your room at least once every 5 minutes. Based on years of experience, BGH feels that you should try to replace it every 1 to 3 minutes if you are trying to cool your room as well as vent it. The formula used to determine the volume of your room in cubic feet is to multiply length x width x height, so a 10 x 10 x 8 room would be 800 CF. Divide this number by 5 and you will have the minimum CFM (cubic feet per minute) fan required to vent your room (in this example 160 CFM).

Not all CFMs are alike
It is important to realize that you cannot compare fans based on their CFM rating alone. Centrifugal fans are by far the strongest and generate the greatest static pressure, which means they can blow through long duct runs without losing too much flow. Squirrel cage or shaded pole blowers (i.e. Dayton blowers) are a distant second, followed by Suncourt In-Line fans and finally Axial fans. Axial fans should only be used for very small rooms or grow boxes where they are attached directly to the wall with no resistance or ducting involved. Suncourt fans are better but dont generate much static pressure, so they should not be used in situations where there is much resistance due to bends in the ducting, insufficient intake source in the room, etc. They are also good for boosting flow down a duct run when the existing fan isnt cutting it.

Things to take into consideration

There are several factors to take into consideration when choosing your fan. The following is a list of things to avoid, or at least factor in when you are choosing a fan:

  • long duct runs the longer the run, the more CFM will be lost
  • sharp bends in the ducting try to use sweeps instead
  • reducing the intake or exhaust going from a 10 fan down to a 4 duct is going to severely impact your CFM and cause additional wear and tear, electricity usage and noise due to back pressure and resistance. When air-cooling lights, for instance, try using Y adapters and reducers to go from 10 down to 2 8, then down to 4 6, an so on.
  • too small of an intake opening in the room you dont necessarily need a fan on the intake side to bring fresh air into the room, but you at least need an opening equal to or greater than the diameter of the exhaust fan you are using. You cant suck air out of a sealed room!

Search FAQ

Select this option if you would like your search to look in the text of FAQ items as well as their titles.

Select an option here to specify how you would like your search query to be treated. 'Any words' will return the most numerous but possibly least relevant results, while 'Complete phrase' will return only results that contain exactly what you are searching for.