HYDRO How do you keep your RH down?

[Dannyboy58]

I'm growing too many plant in a one tub hydro setup and having trouble keeping the RH down inside the grow tent. I have a small room humidifier, which collected almost 3 cups of water in the last week, in the tent as well as a 6" fan and can't get RH to drop below 60. Ordered another fan but don't have high hopes that will help much more. Plants are in flowering and afraid of bloom rot or mold in my buds.

Any suggestions appreciated!

[GreenAlchemist]

Honestly I’d upgrade the dehumidifier or add a second small one to help out. I’m dealing with Powdery Mildew myself, so low Rh% is a must!

Personally have 2-3 dehumidifiers running throughout the room/in tents, loads of airflow, and always make sure they are empty when you go to water/feed (incase they auto shut off from being full)

[Dannyboy58]

2-3 dehumidifiers of what type? The one in my tent is one of those little desktop ones. First time I've ever used one. It definitely fills up so it's collecting moisture. Just not big enough for the tent I guess?

[GreenAlchemist]

I’d definitely add another then or upgrade if it’s a small desk top. It’s workin pretty hard pulling all the moisture out by itself. What size is your tent btw?

I’ll include a photo of the one I use myself. Keeps my 20’x18’ room at about 30-40 Rh% constantly running with the other smaller one. I recently upgraded to a larger one on an AC unit, but that’s when I really need the extra power.

[Dannyboy58]

huh...my dehumidifier is actually rated for slightly larger space than yours but won't get my 4'x4'x6.5' grow tent below 60RH. Maybe I should try your brand and see if it works better.

[Dannyboy58]

yea mine is rated for about the same amount of space as that one. I just ordered another one for about the same size area. See if two can lower it a bit. Adding another fan as well later today.

[GreenAlchemist]

yea mine is rated for about the same amount of space as that one. I just ordered another one for about the same size area. See if two can lower it a bit. Adding another fan as well later today.

That should do it!
Rh% can be a pain to dial in correctly. Let us know how it goes after couple days, it should definitely bring it into a good Rh zone.
hopefully we can help lower that humidity you

[Dannyboy58]

The tent is in an unfinished basement space but there's an AC vent right in front of the tent. I've always kept it closed because the space is unfinished. I think I'll open it and see if that helps as well. May dry out the air in the room a bit which is probably one of the dampest places in the house but it does get good ventilation with the air handler right nearby. I feel like I'm rambling...must be the killer queen...

[Catfish22]

That will probably do it. Give it a couple days to dry out the room.

[MagicMike66]

Get a better dehumidifier. Can’t remember the tank size of mine but it’s a good few litres and it can easy fill that twice a day when it’s needed inside a 1200x1200mm tent

[Rojofresa]

Cover tops of your system with plastic bags or any other opaque sheet that doesn't let light in. That should drop some evaporation down and lower your RH

[Dannyboy58]

I did notice a big increase in RH when I cut an access hole in the lid. I keep it covered with a net pot that has aluminum foil over the top but that change definitely increased RH in the tent. I wondered if ti would help to cover everything with a sheet of black plastic?

[Rojofresa]

Another thing to take in consideration is that your plant growing in mass and surface area getting bigger also equals to higher RH%. To solve issue like that will take stronger ventilation but if that air is circulating in same area it will slowly but surely increase over time, so you would have to get that moist air out and dryer air to your grow area. Another and the easiest way is to get a bigger dehumidifier that can actually dry faster the air than the plant releasing moisture. You could try to find formula to calculate how much water needed to be removed from the air to lower your RH% to the preferred level. But RH% being in 60% is not that bad, not huge risk for issues, but you should just take care that there is enough spacing between your buds and maybe defoliate if it's getting stuffed in your grow area. If you can try to seal your hydro with plastic wrap or bags so you can minimize the leakage from your hydro at least, even squeezing few % off would bring you to the safe side!

Hope this helps you!

[Dannyboy58]

Rojofresa I was worried about the RH because I heard it should be below 50 and preferably 40-45 during flowering so the buds don't get mold or mildew? My NLs are 4+ weeks into flower now. One was pretty heavily defoliated, the other more lightly but they're pretty open. My Afghans just started to flower last week or so and are bush as heck. I'll defol them more in a week or two and hopefully be harvesting ast least on NL in a couple weeks. which should also help.

I'm in northern VA where it's pretty humid and the grow tent is in my basement storage area which unfortunately is probably the most humid room in the house since my well water conditioning system and sump pump are both in that area. I opened another bigger vent on the back of the tent yesterday to get more air flow but the room is at 57% RH today so that's not going to help much. Guess I'll have to spend more and get an oversized dehumidifier.

[gbauto]

Danny, I try to use a VPD chart to guide my RH % during the grow.
You didn't mention what type of lighting you're using, but I typically run above 50% rh@ 83 deg room with led's during flower and closer to 65% during veg..
The best weapon I've found to prevent PM is plenty of air movement in the room.

[Dannyboy58]

LED, ViparSpectra 2000. Operators manual said 18-22" from plants at 100% but that was burning them. It's now about 22" above the tallest ones at about 80%. I have two 100W LED grow bulbs pointed at the snorter plants at about 18" to supplement. Heat hasn't been much of an issue. Temp has stayed low to mid 70s. I have two small fans in there now and can easily crank them up a little more. I think the larger screened vent I opened lets more air in as well but it's not helping with the RH so that may get closed back up since the air coming in is higher RH than my preferred target. Good to hear it hasn't been that much of an issue for you.

gbauto thanks for the tip on the VPD chart. I'd never seen it before. Very interesting and I'm solidly in the green so feeling much better about the situation.

[Dannyboy58]

Got this top Amazon rated pro breeze today. I'm not particularly worried about the RH in the grow tent after looking at the VPD chart but I will need to get it a bit lower to dry my buds after harvest so figured I'd continue the search for a better air dryer. The probeeze has a much bigger tank and makes pretty impressive claims about how much moisture it collects. It's definitely the most well made and substantial of the 3 small dehumidifiers I currently have. My original is going back to amazon ASAP. My first one collected maybe a pint and half of water in a couple days, the second one has been in there since yesterday afternoon and has a couple ounces in it.