Fertigations and Humidity

[Rhizoma]

Hi everyone
Again humidity issues!!

I change to Coco coir 100%
Currently at 3 fertigations per day 2min each automated topspin 12 dripping, with runoff of 10-20%
280w LED In a 2x4 tent with 3 X 6.5l pots and 2 X 3.5l pots.
Humidity outside is around 70% - lung room 65%
Humidity in the tent is around 65- 70% light on (temp 27-28C) and 55-65% light off with dehumidifier on (temp 23-25C).
I am starting week 4 flowering so from now I should reduce RH.
Surprisingly I have very high value during light on and I am not sure what to do.
Should I reduce fertigation time? Maybe 2 at 1min instead of 2min?
I would like to avoid to run the dehumidifier during light on for cost and temperature.

I have already increased extraction and over this I will reduce a lot temperatures so I would like not to touch.
I have 3 6" oscillating fans (2 top 1 bottom) 24/7

Any advise would be very much appreciated

 

[Ca++]

Could you bring your air in the bottom, where it gets two fans. Then let it come up through the plants due to the extraction, and reduce the air movement above. The idea being that all the water the plants make, leaves as directly as possible.

Two fans up top might be sending damp around, that could of left. There is also the angle that blowing on the plants increases evaporation.

If temperature has to suffer, then I would choose that over high RH. High RH can loose you all the big buds. Especially if you are going north of 9 weeks.
I see your outside RH is actually 70%, which might mean more extract can't lower RH anyway. It's only lower in your tent, as the air was heated. I can see why you asked for advice. 7am here.. so I may need to come back after some sleep. I suspect the dehu will be needed. You have room for more temperature, without if being terrible

 

[Rhizoma]

Two fans up top might be sending damp around, that could of left. There is also the angle that blowing on the plants increases evaporation.

Firstly many thanks to take the time to think about my case and reply.

I would prefer to have them to move the air around the buds, the main colas, that is where I am more concern about mould.
But considering I don't want to buy a new fan and that I have a cloud dry I put it over 6 which give me good movement under the canopy ( shaved).

My point is:
- with 3 fertigations at 2 min I am relatively saturated 80-90% and this should be good with Coco, but also means I have always 37l of water/humidity around.
Also with dehumidifier I am very in the limit as the space is constantly humid...

Normally when I start dehumidifying with HPS and soil at week 4, RH drop down day by day, week after week...but with Coco and Led now I can notice that this is not the case and after 1 week still I have values above 60.

I have several time more Rh inside the tent that outside the tent
Now ( after 12 h of dehumidifier)
63% inside
61% lung room
79% outside

Temp at light off are 24-27c now at light on 27-29c

I have put the fan to 2 as min also when light off...

Important also:
Before if I were opening the door outside the grow room ( i mean outside the lung room) and taking air from outside...RH was dropping down very fast...up to -10%RH.
Now nothing.

Also my EC runoff is just +300ppm which is telling me that actually 4 or 5 fertigations should be better....and I assume this will increase the Rh.

 

[Ca++]

I have several time more Rh inside the tent that outside the tent
Now ( after 12 h of dehumidifier)
63% inside
61% lung room
79% outside

Does your dehumidifier shift more air than your extract? Sat in your lung room, is it blowing out air around 50%?

If you can have it blow that 50% air straight into the tent, the lung will increase from 61% towards your 79%. As the tent drops RH.
This might seem like there is no gain, but the dehumidifier works quite a bit better as the RH it's dealing with increases. Even stood in that 79% it will be blowing out air under 61%.
If you stop mixing the dehumidified air with the lung air so much, and instead get it straight into the tent, the overall efficiency will increase.
The balance between extraction speed and dehu delivery speed would be a big issue here. You don't want to duct the dehu to the tent, but rather have it blow at the tents air intake. Avoiding any positive pressure problems a slowing extract might create.

I presume your extract leaves the building, and doesn't ever come back around. That this 79% is because it's constantly raining or something.

 

[Rhizoma]

Does your dehumidifier shift more air than your extract? Sat in your lung room, is it blowing out air around 50%?

If you can have it blow that 50% air straight into the tent, the lung will increase from 61% towards your 79%. As the tent drops RH.
This might seem like there is no gain, but the dehumidifier works quite a bit better as the RH it's dealing with increases. Even stood in that 79% it will be blowing out air under 61%.
If you stop mixing the dehumidified air with the lung air so much, and instead get it straight into the tent, the overall efficiency will increase.
The balance between extraction speed and dehu delivery speed would be a big issue here. You don't want to duct the dehu to the tent, but rather have it blow at the tents air intake. Avoiding any positive pressure problems a slowing extract might create.

I presume your extract leaves the building, and doesn't ever come back around. That this 79% is because it's constantly raining or something.

Many thanks!
This I guess Is part of the problem.
I have actually forgotten to mention.
The dehumidifier is located on fron of the tent which is slight open blowin air inside the tent directly.

Previously ( normally) if I was setting the dehumidifier at 65% the lung Rh was as such but thentent inside was 55-60% RH.
Now is not anymore the case and actually is high inside.
Now it is set at 55% and I have 55-65% in the tent.

Dehumidifier at light on is not possible as temp are already 28-29 close to 30C

 

[Ca++]

You might be over cautious regarding temperature. At 30c you leaves are perhaps 27-28c which is just about maximum production. This maximum production peak can be a couple of C either way. It's something you can miss by a couple of C, without disastrous effect. There is a common school of thought surrounding the loss of voc's at high temp, but it's using over 35c before it's getting serious. Some people work with 40c every year, while others find it unthinkable. Just as some like 21c, where I personally find nothing happens. Perhaps you should give it a try and get some numbers. The extra heat will reduce RH, and the extra extract from that heat will reduce it to. I just worry about extra extract drawing in more 79% to deal with, and if the dehu can process it

 

[Rhizoma]

Thanks!!
Extractor is set at 28c and I will adjust at 29c but also it is set at Rh 65% so go up crazy whem humidity is high.

At light off I am at 24-27c but even at 27 I can have 65% if not more...

I forgot to mention that yes I am extracting outdoor.
The dehumidifier 12l warmed well in soil and hps...but just soil where the dry wet cycle help to keep Rh down. But Coco with 10-20% fertigations 3 times + led + location....
The point is that location is the same problem for several people...so there is something else I could do.

Let's see with temperatures

Many thanks again!!!