Help w CO2, on/off times, exhaust off times.. please read, i need advice

So some of you have already helped me with some info on this matter. but after research and looking at my bank account heres what i'm thinking of doing, let me know what you think.

At this time i cannot afford a CO2 meter for $300, nor can i afford a AC unit.

I have a 96 cubic feet room, w two exhaust fans, cool tube and im 2.5 weeks into flowering. i have a CO2 w flow meter and reg.

so im thinking of turning on the Co2 tank for 4mins and shutting the exhaust fans off for 2hrs. then turn them on for 2 hrs. then pump co2 in again for 4mins and exhaust fans off for 2 hrs. then turn them on for 2hrs and so on until i reach all 12 hrs of lite. i know i cant get an exact reading with out a meter, but i think i can avoid fucking the girls up if i start w small increments, and i wont burn them if the fans are off for only 2 hrs. i dont mind the expense of refilling CO2, which is like $30 opoosed to $600 min for ac and co2 meter.

what do you guys think? any other ideas? anyone run co2 into a grow room near my size 96 cu feet and if so how long do you usually fill the room with co2?

Thanks for your help in advance

I think you're better off using NO co2 than using unmetered co2. Too much is bad and you have no way of knowing what you're doing.

Can you afford a co2 PPM meter the kind that sticks on the wall but doesn't actually control the tank?

CO2 is like the last thing you need to worry about after you have optimized the rest of the grow. Do you have the best lights possible, etc?

Is that room sealed, is that why you want it? I'd just pull fresh air in on a regular basis, whatever doesn't interfere too much with your a/c.

Just my opinion....

im always pulling in fresh air, i have a big oscalating fan in there. ill have to search a co2 ppm meter and check the price. i have a 600w hps, sealed room. just nned to caulk the seems of the wall, but no biggie.

anyone else have any ideas?

That schedule will work if you can keep your temps under like 87degrees the entire time. I run a similar schedule right now, but my exhaust is only off for like 30min. I can't keep my temps under 90degrees for much if any longer than that. I have a 600watt a/c light, but I don't have a great fan cooling my light, so you may be able to do it for longer.
Try kicking off your exhaust and see how long you can keep it below 87degrees with the fans off. Remember that sometimes when the fans kick off, it will be warmer than other times. Like if your house a/c just kicked on, and you are pulling a bunch of cold air inside, your cab will stay cooler for longer. Figure out what the max temp is that your cab gets to with the exhaust on, then see how long it takes for it to get up to 87 degrees from there. This will be how long your want your fans off.

bongrippinbob said:

That schedule will work if you can keep your temps under like 87degrees the entire time. I run a similar schedule right now, but my exhaust is only off for like 30min. I can't keep my temps under 90degrees for much if any longer than that. I have a 600watt a/c light, but I don't have a great fan cooling my light, so you may be able to do it for longer.
Try kicking off your exhaust and see how long you can keep it below 87degrees with the fans off. Remember that sometimes when the fans kick off, it will be warmer than other times. Like if your house a/c just kicked on, and you are pulling a bunch of cold air inside, your cab will stay cooler for longer. Figure out what the max temp is that your cab gets to with the exhaust on, then see how long it takes for it to get up to 87 degrees from there. This will be how long your want your fans off.

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ya, tonight i will be home watching the opening kick off and i will see how long i can leave the exhaust fans off. i planned on doing that anyways. i may have to adjust the timing but ill run the test tonight and get back to you. usually i can run my exhaust and the temps dont go over 83, but with them off, like you i may not be able to have them off that long. ill check it out tonight

If they are sitting at 83 degrees with the exhaust on, I am going to say you will only get about 20-30 min of exhaust off.
Make sure you are checking the temps at canopy level so you know that your plants are not frying under the lights.

tonight i turned the exhaust off and sealed up the room. i added a 16" wall mounted oscaliting fan. but i had the exhaust off for just over 2 hrs until it reach 86. however the humidity was at 72. i opened the door after the 2hrs for about 3- 4 mins and the humidity dropped to 58. what should i do about the humidity? get a de-humidifier??

I suggest you just flow air through there. Is there any reason you need to leave the fans off?

-=4:20=-Guy said:

I suggest you just flow air through there. Is there any reason you need to leave the fans off?

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will the exhaust fans... would suck the CO2 out of the room. thats the reason for turning the exhaust off.

Do you have an air cooled fixture for your lamp (I assume you do), if so what is the cfm on the fan that you are using to cool it. Also is the exhaust for your fan a closed system, i.e. does it pull air from outside of the room through the light and back outside of the room or are you pulling air from the room through the lamp to exaust. If you get a relatively high cfm fan for your lamps exhaust and use a closed system then you should be able to keep the seperate exhaust of the room to a minimum, many people don't exhaust at all during lights on when they use co2.

I am in a similar situation. I had my grow rooms just how I wanted them and was using a fermenter to introduce low levels of CO2 on a constant basis in the flowering room. It was cheap but inefficient. A friend brought me a CO2 regulator with a solenoid on it and asked me if I could use it . He wanted nothing for it. OK, I guess I will take a chance and see what I can do with this. Where I work we do industrial processing and use tons of bottled gasses. My gas guy gets me a 20# tank of CO2 for $10.00

I could not lay out the money for the high tech PPM meter or a CO2 controller at the time so I went to my hydro shop and got some black tubing and drilled tiny holes in it about every inch. I created a ring with the tubing that I hang from my light. I set up my timers to turn off my recirculating fans, carbon scrubber and fresh air intake for 2 hours. During this time I turn on the solenoid on the CO2 tank to dispense the CO2 at a rate of 2 cu ft per hr for 90 mins. After the plants have had an extra 30 mins to soak up the CO2 the timers turn all the other equip back on.

I am using 400 watt HPS and my highest temp in 24 hrs is 84 F. This has worked for my last grow and I was thinking about increasing the rate of delivery or possibly the length of time for delivery with my current grow which I triggered on Aug 28. It isn't scientific but it is working reasonably well so far. I need to get a PPM meter or controller but it is out of the budget so far. My Relative humidity is staying between 40 & 55%.

Did you use a Co2 calculator to figure out how long to have your Co2 on for Tommy? Depending on how big your space is, you probably don't need the Co2 on for 90min. It only takes like 4min to get my 100cu ft cab up to 1800ppm. You may want to check on that.

As far as your humidity goes, it looks like the only thing you can do is get a dehumidifier. Or maybe just have your fans off for a little less time. Maybe like 1 1/2 hours instead of 2 full hrs.

regrets said:

Do you have an air cooled fixture for your lamp (I assume you do), if so what is the cfm on the fan that you are using to cool it. Also is the exhaust for your fan a closed system, i.e. does it pull air from outside of the room through the light and back outside of the room or are you pulling air from the room through the lamp to exaust. If you get a relatively high cfm fan for your lamps exhaust and use a closed system then you should be able to keep the seperate exhaust of the room to a minimum, many people don't exhaust at all during lights on when they use co2.

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i believe i have a 50cfm, that is pulling air from outside of my room through closed duct work and then exits out my room. it was a left over fan, i could always upgrade, but it seems to serve its justice.

Like ive said before, im not going to run the exhaust when Co2 is on. unless i upgrade the cool tube fan or get ac, ill have to turn the exhaust fan on and off a few times during the 12hrs.



Thanks for everyones input, i gonna turn it on tonight. ive got my battle plan in order

50 cfm is very low, and if you get a higher cfm fan the temps in your room will go down because the hot air will be taken out and then you can run your co2 longer, also if you get an air cooled reflector this will greatly decrease the temps in your room and you can leave the ventilation for the lamps on while you run the co2 in your room if you have it on a closed system. The combination of these two upgrades will really make it worth it to use co2 because you will be able to run the co2 longer and keep your ventilation off longer. It takes time for your plants to absorb and use the higher co2 levels and constantly cycling the co2 out of the room not only wastes co2 but your plants don't reap the full benefits either. The less ventilation you can run during lights on the better, which is why if you are going to invest in co2 you should definately invest in an air cooled reflector and some good ventilation fans. Just my 2 cents though. Good luck.

As long as you can keep your temps under control I would just nuke it at each fan interval. I don't really see the need for Co2 in your situation though, I would just keep fresh air circulating.

Haven't you heard our air contains more Co2 than ever =)

It does contain more Co2 than ever, however, it is only at about 300ppm in natural air and plants like it closer to 1500-2000ppm. So we are about 5-7x shy of what we need.

Cheap DIY controller

International Cannagraphic Magazine Forums - DIY CO2 PPM Controller

Or even better

Let It Grow Hydroponics : Hydrofarm ActiveAir CO2 System (1-20 CFH)

He already has one of those to fill the room. He just needs to know how long it will take for his plants to use the Co2, when to refill the room, and when to exhaust. He already knows how long to run that system to get his PPM up to 1500. He is trying to get his cab to stay at a steady 1500ppm, or at least get the most out of what he is using.