High temps in lights out

Hi everyone, just bought and installed my pulse pro last week. Loving this thing just trying to dial everything in.
Had to put my dehumidifier in my tent for lights out as humidity was getting to 70%+ ,
Now my night temperature are 83 - 84 and my day temperature are anywhere from 79-84.
Anyone know if this a problem?

What stage of growth?
What type of lights?
Autos or photos?

Also, run your lights at night this will make it easier to control your heat if you don’t have ac. 60% to 75%rh in veg is perfect, 40% to 55%rh for flower is perfect. If you run CO2 85F is fine

Thanks for the reply’s
I am running 2x600 hps and I’m at around 4 weeks of flower . Photos, never tried autos.
My lights on temp 79-84 Rh 50-55%
Lights out it used to be before I got my pulse so I didn’t know till last week was 70ish with a Rh 70-80%, so I’ve been trying to get Rh to stay below 60% for the whole lights out but its been a struggle so far. I had to put my small dehumidifier right in my tent. But I had to put it on continuous or it would come on and off almost 10 times per hr. So that brought my humidity to around 40 but my temps go up to 84 which is as hot as my lights on high.
And I’m not running co2 but the week low is 930 and my avg is over 1500

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In a 4x4 i run a 30 pint dehu and it is borderline for me to stay in the high 40’s to mid 50’s for rh. Any smaller of a dehu is a waste but I don’t know your room size.

Remember hps generate a grip of heat and when lights go out you are going to see a massive rh spike and you may chase it for an hour or two.

You can use ac if you have a window unit feeding the tent via a tube to help get the spike down. I use a 16,000 btu window unit for my 4x4 and it helps a ton, not to mention when i go to dry it helps lengthen the dry time.

The golden rule for nightime temps is no more than a 10F swing, I run about 5-10F during lights off, but again I don’t run my lights during the day. Lights on at 8pm and off at 7am.

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I’m in a 5x5,
My dehumidifier kept it at 40 pretty good when it was on continuous but it filled up 1 hour before lights on. So humidity got up to 61% … not to bad but still over the dreaded 60 %.
Tents in my basement and I have a bigger dehumidifier(50 pint) in the basement as well with the smaller one in the tent think it’s a 30 it’s 500 watts I think, the bigger one is over 800 watts

So your outside environment is really important for your tent. I know people freak about anything over 60% because of botrytis bit you can offset that by temp, truth be told I have grown in 70% while in flower with no issues, dew point is the main factor in it all. However those conditions are not ideal but neither is growing when it is 110F outside either right? It’s all about the environment and you make it work for you.


Just following along trying to learn something. Curious what are HPS lights and if you’re not using any type of CO2 generation how is your CO2 so high? I’m using one of those CO2 generator bags and can’t get the CO2 higher than 600 ppm. I’m told I have to add another bag or two to get it up there.

I think the co2 is high because there’s 4 people living in my house and there’s almost always someone home and for most of the time 3 or 4 people are usually home. I guess we are all just little co2 generators. I use those bags as well. But I was on another forum where a member did an experiment with the bars and come to the conclusion they don’t do anything noticeable to the co2 level. Don’t think he tried multiple though, so good luck if you try more than one hopefully it works. A few years ago I used the bottles of co2 that you shake up, also made my own. Not sure how much compost they let off.
Hps is high pressure sodium, it’s the type of lights everyone used to flower with before LEDs.

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Do you have an exhaust fan? On top of the dehu I would have a fan exhausting 24/7. It helps stabilize your conditions. Tbh I don’t think you need to bring it to 40 at night . That’s a bit of overkill in week 4 imo. 55-60 is complete fine for nights . Try raising it a bit and see if it helps. And I would turn it off continuous. The cycling is pretty normal in a garden. But sometiems cycling happens from a dehu that isn’tt sized correctly .

[quote=“Sargentd1, post:8, topic:891”]

Buying those bags a few times could get you a decent DIY co2 setup for the cost.
Part of why it’s soo high can be
If he has family and an air conditioner, the family will create co2 as they breathe and the Ac circulates it around the house . . I’ve recently seen this in action when my friends and their 2 dogs went away and my co2 dropped to below 500 from 1200. It’s crazy how much co2 comes from breathing and pets . The other reason can be if you have any gas appliances, they have a pilot light that burns small amounts of gas where the byproduct is CO2 .

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If I don’t have my dehumidifier on continuous it comes on and off almost 10 times an hour, eventually it just shuts itself off after a couple hours of that. So that means my dehumidifier is the wrong size? What size dehumidifier would you put in a 5x5 tent?
I don’t have a fan exhausting off the dehumidifier, I have my exhaust for the tent hooked to my carbon filter plus a fan hooked to my cooltubes separately from the rest of my tent to cool the hps
Plus multiple fans in the tent for air circulation

I see what your saying… it doesn’t mean it’s sized wrong. It’s just a symptom of a incorrect sized dehu. But that doesn’t mean your is. That’s weird it shuts itself down. I’m guessing from the compressor getting hot? There’s a calculator your can use to figure out your dehu size needed. Let me find it for you real quick. But try bringing the Rh up to 55-60. It’s not that big of a deal to run 60 at night when your temps are not too cold. You def don’t need 40% Rh at night. I can promise you 60% will not bring you mold when you have proper air circulation and and exhaust running 24/7 and a dehu.


Here is the dehu calculator

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A few times I have noticed the start of mould forming on the inside one of my denser cultivars(orange dots inside bud close to stalk) . This has happened a few times over the years. I always have lots of fans and air movement .
Now I got the pulse and am seeing the humidity get up to 80% sometimes when lights go out. So I want to just get the humidity under 60 during lights out.
Without dehumidifier at night temperature are about 70 with 70-80% humidity, so I’m thinking that’s how the mould has been getting started.
Thanks for you great response. I appreciate the help.
And thanks for the dehumidifier calculator.
I’m using blumats so I usually put 1 home depot bucket of tap water into my res every 2 days.

First I tried to just set the big dehumidifier on the other side of the basement and had the smaller one right beside my tent but the smaller one would fill up after like 6 or so hours and then the humidity would steadily climb to 70%

Thanks for the reply, when I get home I’m going to hang another one of those CO2 bags. See how it goes, I have another son that has a 3x3 tent he made his own CO2 generator with 2 bottles and some silicone hose. 1 of the bottles has a mixture of yeast and ??. The other is clean water that the CO2 filters through, he had his CO2 ppm up to about 1300. If the other bag doesn’t do the trick I’ll have to try the home made yeast method.

Ya I can definitely see the cost of those CO2 bags adding up. I was on Amazon looking at some options, but I’m not going to rush into anything this late in my grow. But I’ll be ready for the next grow with something that will work much better than those bags.

Thanks :blush:

I’m really suprised the yeast method produces 1300 ppm . How long can that yeast method hold that saturation ? I use a cycle timer and a 120v 1/4” always closed solenoid hooked up to a 20lb tank. It gives a 5 second shot of co2 every 30 mins and that keeps me at around 1200ppm. I’m not in a sealed room and this is just something I’m trying . Your psi off your regulator can also be used to control output. It takes a little bit of dialing to get it where you want it . Good luck