Humidity problem with rockwool blocks in sealed environment?

Indoor Growing Hydroponics
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I think I have humidity problems.

I have two rooms. One for flower (ebb and flow SOG with rockwool) and another for mother and clones. One fan connects the airflow of the two rooms.

My dehuey sits in the mother and clones room and runs now constantly to bring the rel. humidity down to 60% in that room.

The dehuey has around 500 - 600 watts. I measured yesterday and I produced 30 Liters of water in 24 hours.

I do a SOG with many small plants, which means many small rockwool blocks and my tables are not covered by some plastic sheet. Before when I didnt run my dehuey 24/7 I got white mold on my rockwool. I killed the mold with 3% h2o2 and also put h2o2 in the reservoir.

  • Is that white mold dangerous for the plants?

Because of temps I will need to switch to external air I guess. But I am thinking already about winter when I will run sealed the whole grow…

  • So how could I keep the humidity in check (in sealed environment), because I think probably in flower my buds might rot away? Because of the ebb and flow tables the humidity in the flower room seems to be higher. I am not sure if I could get it down to 60%.
  • Should I put some plastic sheet over the tables which would act as a humidity barrier? Then would I get mold under that plastic barrier? Also problematic is that it means I could not change the postion of the plants anymore. I am not sure how much space they need.
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I’d say a bigger dehumidifier than what your using or extract your room at lights out ! I know it defeats the sealed room purpose but your better to have non moldy bud than a total mess with too much humidity!

I’ve been there the whole fighting to keep humidity in check is simply solved by a big enough humidifier for the room,plenty of fans also help to keep things fresh and diminish moisture gathering on leaf surfaces!

A simple extraction fan on a inkbird controler set to run when the humidity rises helps a lot also winter your choices are limited but winter it’s usually not as humid as summer plus it makes for some colorful buds giving them some frozen air at night lol

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So the humidity problem happens especially at night when the temps drops?

So are you using CO2 now and extracting at night?

Might be worth considering, unfortunately it would mean I would need to change my system with sealed time controlled ducting flaps and more ducting. The flaps would open at lights off and close at lights on so it switches automatically from internal to external air without letting the air escape to the external when lights are on. At the moment I can run only internal or external air. For switching I need quickly manually change the plugging of my ducting. But having both systems at the same time, internal at lights on and external at lights off I am not sure what is the easiest way to do that.

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Yes I’m running c02 as well , a fix I’ve come up with is a simple 24 hr timer set to come on at lights out running the extraction fan you can play with the setting and have it come on every half hr run for 10 min or what ever time you need to get humidity in check!
Inkbird does the timing for you !

At present I’m removing roughly 17 gal of water in a 24 hr period keeping my humidity in check not including what the AC removes while running , guessing another 3/5 gallons it collects daily. (28x32 room )

At present the room stays sealed for the simple fact I’ve enough dehumider to keep up but if not the extraction fan using the inkbird will fire up and play catch up!

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My last run I was in the same boat, humidity was out of control and my dehumidifier couldn’t keep up.

I had a great exhaust fan so I went w/ the timer method to keep it under control – but I found that I hated the lack of control. Either I was running it too long or too short, or it would get super humid during a different time of day. I also had to constantly adjust to keep it where I wanted it and found it annoying, but I was able to do it using parts on hand and “it worked”.

I ended up switching near the end to a cheap Inkbird humidity controller and that was a whole lot better.

This run I’ve updated to a new AC Infinity fan w/ the built-in temp/humidity controller. So far I am loving this setup. Now if it only had Wifi I’d be set.

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You would be better switching it the other way round so the humid air goes into the mother clone room from the veg/flower room. Clones and cutting need a higher humidity as there roots are not developed. That’s how I ran my Veg and clone mother Cab with one extraction fan.

Humidity is relative to temperature. The more you can keep the temps together from lights on and lights off the less your humidity will fluctuate.

You dont use CO2 at night/lights off, so you can run your extraction or dehumidifier then.

Heres a VPD chart for you, you need to keep your temps and humidity in the green band.

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What you said I should switch? The air circulates at the moment between the two rooms. And the dehuey is in the mother/ clones room.

How does it work with Co2 and an extraction fan so the co2 doesnt escape through the ducting of the extraction fan when the lights are on?

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I said you would probably be better having the dehumidifier in your flower room, not the mother clone room. As clones and cuttings need a higher humidity. Between 65% to 75% which is normally too high for flowering in.

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ok. at which point in the room I should put my hygrometer? At the moment I put it on a rockwool cube. But when it is there humidity is always 65 to 70%. Even if the dehuey is running constantly. So maybe the dehuey is too small or measure at a different point (maybe the rockwool cubes moisture is interfering with the measurment) ?

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It could be that.

Your temps and humidity will be different, in different parts of your room. My hygrometer hangs at canopy hieght, where the majority of leaves are, in the middle of the room, and is adjusted as they grow.

In winter I use passive air intake with an extraction fan and a heater at night

In early summer I run a semi sealed grow with a window air conditioner, re circulating the air, my CO2 supplement comes from my home made wine, that ferments in the room.

The air-conditioning keeps my room at 78F and RH at about 45% to 55% lights on, when lights are off, the aircon just runs as a fan, and my extraction unit comes on, if RH climbes over 60% and or temps around 70F.

When we hit full summer the air-conditioning runs 24/7 and the air extraction gets turned off completely.

Like most grows, where money is restricted, you are going to have to experiment a bit and tweak it about, to get it near perfect. Until you can afford a dehumidifier/aircon unit in each room, as seedlings and clones, veg and flower rooms need different environments, so until then compromises are needed.

I live 9 kilometers from the sea so our temps and humidity fluctuate greatly on a day to day basis, where you are it’s going to be different unless you live near me. Every time I change some parramatta in my grows, I have to start dialling it all back in again.

This is just my 8x8 ft flower room running 2x600w HPS lights, my veg and clones run LEDs so the heat and humidity is less an issue and can be delt with easier.

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So I have 84 Fahrenheit or 29 degree celcius in my room. I need to have a humidity level of about 80%?

Will that much humidity not cause my rockwool to grow mold and my buds to rot?

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For flower I’d say too high you’ll need to lower temp to get the vpd lower to run humidity at around 60% max ,that’s just my thoughts maybe I’m way out to lunch but experience with high humidity in bud can and will cause mould and mildew leading to bud rot stock rot .

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According to the chart, 75-80% humidity. As someone pointed out it’s a guideline. Different strains have different preferences. Your chances of developing mould are higher.

Me personally I would keep at 65% max for my grow in veg, 55% max for my flower room and around 75% for my clones and seedlings.

I don’t grow with Rockwool, or use flood and drain. So I couldn’t say for sure if that humidity will cause mould, it would certainly be higher chances of it it developing. I would definitely be worried about powdery mildew though.

I grow in no till organic soil, I don’t have high temps, and high humidity, unless something goes wrong.

With a lower humidity my plants grow faster as they uptake more water and nutrients when experating, but with flood and drain and bottle nutes, you have a higher risk of burning your plants quickly, growing that way.

The only way to know for sure is start growing and work out the kinks, as you go. Which is why people don’t jump straight into a grow with CO2 as it’s more complicated and expensive.

When you have been growing a while you may realize you don’t need CO2, to get great results, taking extra chances of screwing up your grow with high heat and humidity.

There is no cheap ways of doing it, I am about as cheap and redneck as it gets in a grow, I build lots of stuff to save money, and experiment, but you reach a point, where you can’t do that, and CO2 is one of them. The right monitoring, and delivery system is very expensive. I have tried other methods, converting a mason jar into a tiki lamp burner, running on methanol, and at half a litre in 12 hours is not cost effective to extra production. As well as a fire hazard.

My flower room is semi sealed it could operate without the extra CO2 from my wine making, I know because I have tried it both ways, and see little difference.

I don’t allow my heat and humidity to get above the norms now because I have air-conditioning. My CO2 from wine making, is a by product and costs nothing to use. To do it properly will cost a lot of money.

The only way I can see, if you go this route is either getting bigger or more de humidifiers, for each room, or what I have done, use air-conditioning as it gives me better control of both heat and humidity problems in my grow.

Also do more research into it before comitting to it.

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The key word is “guideline”. VPD charts provide optimal growing condition and put you right on the edge of the knife. Better to err on the side of lower humidity and minimize the risk of mold.

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So if I am running at 60% humidity at a 86 or more Fahrenheit, how big of a negative impact will it have on the plants and yield? I read its sub optimal range if it is less than 80% humidity… Or do I have no reason to worry if I run it at such “low” humidity?

  • What rel humidity do I need to have in flower so I will get no mold? Can I differenciate between early and late flower? So if it is early buds dont easily mold, or does it even happen already in the early stages of flower?

  • The white mold on the rockwool, how is it called, and is it a danger to the plants and the buds?

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Better the humidity is lower rather than higher. For a lack of a better way to put it, high temps and humidity can have the effect of suffocating a plant

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I am thinking about switching now to external air completely (which means no CO2). The reasoning for that is I think my dehumidifier is not strong enough (when lights dont get humidity lower than 65%) and I have no time and money to build now an exhaust fan mechanism which will pull out the humid air at lights off. Also I had now to add two more 600w lamps, in total it is 4x600w lamps now and the room runs at 33 to 34 degree celcius.

  • What will happen to the plants if I switch now to external air (400ppm?) when they had their whole life co2 (1500ppm) and high temperatures? I just switched the light cycle to flower. Will the plants be shocked a lot?

  • I am thinking about keeping the sealed environment as long as possible but I worry about mold or pests. At what stage of flowering is there a real danger? Already at the beginning?

  • I am still wondering about something. When you have an exhaust fan which activates at lights off and high humidity, how do you prevent at lights on and fan off conditions the escape of co2 and odour through the exhaust fan ducting? Has it to do with negative pressure?

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Yesterday when I came into the rooms. The temperatures where up to 98.5 Fahrenheit or 37 degree celsius. I decided to switch now to external air.

CO2 meter shows around 500 ppm.

I am wondering now how the plants will react. If they all their life had CO2 supplementation and high temperatures.

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Only one way to find out for sure.

I think they will slow down a bit, while adjusting, so long as the temperature lowers they should cope ok, I would think.

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They might be shocked for a bit but should like the lower temps even if the c02 is low !