Problem with high RH inside the tent

  • Thread starter lilvexed
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lilvexed

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Hello thc farmers!

So a quick wrap up before we get into the subject; Having 3 autoflowers in 3x3x5 tent. Plants are grown in 5L perlite Hempys and one in small 2L coco hempy.
Ventilation: "passive" intake. Fresh air comes from the outside (it's ducted with 125mm tube from the room ventilation to come inside the tent)
Exhaust: 4" Carbon filter and 6" Vents VKO125 inline fan drawing.

So everything was fine until the plants stretch phase slowed down. RH used to be stable 40-50%. Now plants just entered into 7th week and the RH has started to creep up sometimes up to 70%.
Temps are in control between 21-24C when lights on and 19-21C lights off.

I guess the relatively high humidity has messed up VPD and plants do "sweat" aka respirating a lot during lights ON. I've understood when the air being too moist the stomata does not function properly and it causes this kind of tip and serrates being burnt and pointing upwards:
C0BD681B B1E1 437B 90C6 07CE56EE8096


FD4454D7 E25C 4465 AB7D EAD6460C6973


During the stretch phase they were doing fine with 2.1-2.3 EC. Now I've lowered EC down to 1.6-1.8 but the new feed didn't have an effect.

I'm having this kind of cheapo extraction fan on the filter drawing.
1652954297399


And this is what gets me confused. The product description says "max draft 185m3/h" So does this fan actually draw 185m3/h(?) and minus ~15% in airflow due the filter?

So that draft should be enough to create almost a little negative pressure inside the tent (0.9m x 0.9m x 1.4m = 1.1m3 tent volume)
And the weirdest thing is if I plug off the fan the temps will raise up to ~26-27C - So the filter is definitely sucking something, but apparently the moisture wont get ventilated enough. Don't really get this… Even at the duct end I can feel by the hand that some warm and prob moist air comes out, but tent RH wont get stable in between the scale of 40-50% in tent.

Do I need a better extraction fan? Carb filter being used only for about 4 weeks so basicly brand new and the pre-filter looks clear.
Also I've tried to play with the nutes in range of 1.6-1.9 EC and tried Potassium from 290ppm down to 210ppm, no effect. Calcium goes about 120ppm and Magnesium 45-55ppm.

Well I prob forgot to mention something, but hit me with the more spesific questions if needed!
Thanks for the help :)

PS. Plants now on day 44. Looking OK, but every time I open up the tent moist warm, almost moldy smell comes out. Worried about the mold and or pests.
83AF8FBE 3CDC 4C44 85B0 D7B2F1293A48

36DE0BBC 8D7A 49AF BFC1 D0D9051716A8
 
SmokinJo421

SmokinJo421

123
28
Hello thc farmers!

So a quick wrap up before we get into the subject; Having 3 autoflowers in 3x3x5 tent. Plants are grown in 5L perlite Hempys and one in small 2L coco hempy.
Ventilation: "passive" intake. Fresh air comes from the outside (it's ducted with 125mm tube from the room ventilation to come inside the tent)
Exhaust: 4" Carbon filter and 6" Vents VKO125 inline fan drawing.

So everything was fine until the plants stretch phase slowed down. RH used to be stable 40-50%. Now plants just entered into 7th week and the RH has started to creep up sometimes up to 70%.
Temps are in control between 21-24C when lights on and 19-21C lights off.

I guess the relatively high humidity has messed up VPD and plants do "sweat" aka respirating a lot during lights ON. I've understood when the air being too moist the stomata does not function properly and it causes this kind of tip and serrates being burnt and pointing upwards:
View attachment 1246281

View attachment 1246280

During the stretch phase they were doing fine with 2.1-2.3 EC. Now I've lowered EC down to 1.6-1.8 but the new feed didn't have an effect.

I'm having this kind of cheapo extraction fan on the filter drawing.
View attachment 1246282

And this is what gets me confused. The product description says "max draft 185m3/h" So does this fan actually draw 185m3/h(?) and minus ~15% in airflow due the filter?

So that draft should be enough to create almost a little negative pressure inside the tent (0.9m x 0.9m x 1.4m = 1.1m3 tent volume)
And the weirdest thing is if I plug off the fan the temps will raise up to ~26-27C - So the filter is definitely sucking something, but apparently the moisture wont get ventilated enough. Don't really get this… Even at the duct end I can feel by the hand that some warm and prob moist air comes out, but tent RH wont get stable in between the scale of 40-50% in tent.

Do I need a better extraction fan? Carb filter being used only for about 4 weeks so basicly brand new and the pre-filter looks clear.
Also I've tried to play with the nutes in range of 1.6-1.9 EC and tried Potassium from 290ppm down to 210ppm, no effect. Calcium goes about 120ppm and Magnesium 45-55ppm.

Well I prob forgot to mention something, but hit me with the more spesific questions if needed!
Thanks for the help :)

PS. Plants now on day 44. Looking OK, but every time I open up the tent moist warm, almost moldy smell comes out. Worried about the mold and or pests.
View attachment 1246284
View attachment 1246283
I can't remember exactly what it is & I need to buy another Bible. I would strongly recommend picking up a Bible for yourself.
Jorge Cervantes medical grow bible
You'll find the answers 4 everything in there.
Jagged leaves and slightly discolored leaves/burn
All in all tho looks gr8, keep it up
 
SmokinJo421

SmokinJo421

123
28
The rating on those fans is more comparable to the rating on an amplifier for car audio.
U want to look at the cfm=cubic feet per minute and constant airflow will always be on your side. Just not "direct" airflow
Deff want to address this issue before you have more mass developed
 

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