My Humidity spikes when the lights go off

Hi guys, so my humidity has been spiking when the lights go off and I am using a 25 liter dehumidifier right next to the tent and it goes up to 70% humidity when the lights are off even with a decent dehumidifier and I am in the late flowering stage. Today I noticed that 2 of my buds closest to the tent wall were going moldy so I cut the moldy buds off and binned them. Do I need an extra dehumidifier to stop the humidity spiking at lights off or how can I deal with this issue? I am 8 weeks into flower and I am going to chop them next week because I don't want the rest of it to go moldy. Any help is appreciated. Cheers

What setting is the dehumidifier on?

i'd double check your buds you're gonna keep with a scope. usually mold is everywhere.

Tolerance Break said:

What setting is the dehumidifier on?

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It's on continuous. It's on the 35% humidity setting and it's struggling to get below 60% humidity inside of the tent and at lights off it goes up to 70% humidity. I'm guessing I need another dehumidifier? It's a 25 liter dehumidifier. It's 90% humidity outside

What's your rh outside the tent? Is the tent exhausted outside or right back into the room with the tent?

cannabiscrusader said:

What's your rh outside the tent? Is the tent exhausted outside or right back into the room with the tent?

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The RH outside the tent is between 50 - 55%. It's exhausted into the room next to the grow room.

Fish scale said:

It's on continuous. It's on the 35% humidity setting and it's struggling to get below 60% humidity inside of the tent and at lights off it goes up to 70% humidity. I'm guessing I need another dehumidifier? It's a 25 liter dehumidifier. It's 90% humidity outside

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I would get a stronger dehumidifier

Tolerance Break said:

I would get a stronger dehumidifier

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I can't afford it at the minute but on my next grow I will get a 40 or 50 liter dehumidifier so I have got full control over the environment

Is it filling up too quickly and turning off or just unable to keep up?

Tolerance Break said:

Is it filling up too quickly and turning off or just unable to keep up?

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It's just unable to keep up

Tolerance Break said:

Is it filling up too quickly and turning off or just unable to keep up?

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The humidifier it's self is saying it's 44% humidity inside the room on the dehumidifier display. But inside the tent it's 57% humidity right now. Once the light goes off it shoots up to 70% humidity.

What size tent and how packed is it. I lost my last run to mold for being too packed and no air flow. Dehuey on 35% and tent 48%rh and when lights out it went to 80% so I supplemented heat and temp probe so it kept temps the same at lights out and narrowed the rh spike to 10% difference.

I now exaust outside grow room and have intake holes on door to draw in air and dehuey in room. It is stable but have not grown huge plants yet but even if I did, I have fans in every corner and below canopy in a couple spots.

My auto flower on 24/0 has no swings and neither does my photoperiod 6 weeks behind but auto is almost ready to chop, no rh issues. I think density of plants inside tent matters. Hope I dont have to supplement heat and heat up the room, makes it uncomfortable in there.

Hoping I don’t have these issues but looks like you have a similar setup but maybe over packed the space. I aim to have plenty of empty open space in and around the plants to see if I can have the same results on larger scale.

I was having similar results but now that I exaust out and draw in air it seems like the dehuey is just working on the rooms RH and not working as hard but before my set up it was like you are describing now. Do you have fresh air drawing in from somewhere? now I set dehuey to 45% and it is 45% in the tents. No spikes because it is lightly spaced.

Less yield but better than the described prior to my set up now.

medidedicated said:

What size tent and how packed is it. I lost my last run to mold for being too packed and no air flow. Dehuey on 35% and tent 48%rh and when lights out it went to 80% so I supplemented heat and temp probe so it kept temps the same at lights out and narrowed the rh spike to 10% difference.

I now exaust outside grow room and have intake holes on door to draw in air and dehuey in room. It is stable but have not grown huge plants yet but even if I did, I have fans in every corner and below canopy in a couple spots.

My auto flower on 24/0 has no swings and neither does my photoperiod 6 weeks behind but auto is almost ready to chop, no rh issues. I think density of plants inside tent matters. Hope I dont have to supplement heat and heat up the room, makes it uncomfortable in there.

Hoping I don’t have these issues but looks like you have a similar setup but maybe over packed the space. I aim to have plenty of empty open space in and around the plants to see if I can have the same results on larger scale.

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I'm running a 4x4 tent and I have 4 big plants inside of the tent. I could always add a oil filled radiator inside the room to give it a bit of extra heat when the lights go off but I don't have a temperature probe so it would be hard to control the heat from the radiator. I've only noticed mold on the two buds that were up against the tent wall. Hopefully the rest is going to be ok

medidedicated said:

I was having similar results but now that I exaust out and draw in air it seems like the dehuey is just working on the rooms RH and not working as hard but before my set up it was like you are describing now. Do you have fresh air drawing in from somewhere? now I set dehuey to 45% and it is 45% in the tents. No spikes because it is lightly spaced.

Less yield but better than the described prior to my set up now.

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I am drawing fresh air through the window every now and then but the outside humidity is 90% so I'm battling the outside humidity also

medidedicated said:

I was having similar results but now that I exaust out and draw in air it seems like the dehuey is just working on the rooms RH and not working as hard but before my set up it was like you are describing now. Do you have fresh air drawing in from somewhere? now I set dehuey to 45% and it is 45% in the tents. No spikes because it is lightly spaced.

Less yield but better than the described prior to my set up now.

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Should I harvest soon since I have found mold on 1 or 2 buds closest to the tent wall? They are 8 weeks into flower tomorrow

Increasing your exhaust rate will also help to reduce sudden changes in temps and humidity.

It's not so much the absolute humidity that's the problem as it is the sudden changes (temp drops combined with humidity spike allows condensation to form inside the buds, which allows mold spores to germinate)

Fish scale said:

Should I harvest soon since I have found mold on 1 or 2 buds closest to the tent wall? They are 8 weeks into flower tomorrow

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I was going to say, 4x4 is like four 2x2’s and can probably be packed easily with four big plants. I did it first try on a 2x2 and the whole thing molded. By time I saw it on outside, it grew all within the cola from bottom up. Every cola, to where the rest of it wasnt worth it, tainted with mold smell.

I would chop all area effected and chop a couple nugs around suspect areas and if it is clean inside, no white powdery stuff on orange hairs etc, I would push it long as you can. If more spots arise I guess I would chop and start over but with smaller plants or one huge scrog.

I am liking the 2.5x2.5 square footage, hard to over pack a space like that or 3x3. So I am doing two large plants in the 2.5x5. If it were 2x2 I would do smaller plants. I did and so far no rh issues. Heck I am growing in a 1x1 box with no issues late flower.

medidedicated said:

I was going to say, 4x4 is like four 2x2’s and can probably be packed easily with four big plants. I did it first try on a 2x2 and the whole thing molded. By time I saw it on outside, it grew all within the cola from bottom up. Every cola, to where the rest of it wasnt worth it, tainted with mold smell.

I would chop all area effected and chop a couple nugs around suspect areas and if it is clean inside, no white powdery stuff on orange hairs etc, I would push it long as you can. If more spots arise I guess I would chop and start over but with smaller plants or one huge scrog.

I am liking the 2.5x2.5 square footage, hard to over pack a space like that or 3x3. So I am doing two large plants in the 2.5x5. If it were 2x2 I would do smaller plants. I did and so far no rh issues. Heck I am growing in a 1x1 box with no issues late flower.

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That's what I'm scared about. It could be in other colas already but unless I chop a few more off I won't know if it's there or not. So that is Definitely good advice but my yield isn't that big anyway because it's quality over quantity. so I don't really want to cut more off the plant that is affected but I could do if you think it's a good idea.

I have no control over how big they've got. Some phenotype's are smaller but the one that is affected by the mold is a lot bigger. I'm guessing that's down to the phenotype?

The outside humidity is 95% and that's what I am fighting against. When I open a window it only makes the RH rise even more inside of the room so I'm really struggling here.

I'm going to have to chop them soon. I can't risk the whole grow going to shit. I've put months of time and work and hassle and money into this grow and I'm not going to be able to start over again for a long time after this grow. This weed is designed to last me at least a year