Help lowering RH. Dehumidifier already in use.

Thanks in advance for any help. I'm new here and this is my first post, however I've always come to riu for all kinds of questions. I'm now on my first indoor grow though so I figured it's time to just make an account.

So I'm running a 5x5 tent inside of about a 10x12 room. A 600 watt hps air cooled and two 300 watt Galaxy Hydro LEDs(about 130 actual watts each I believe).

A 6" 410 CFM fan and filter inside tent(has a few 90 degree duct elbows, couple bends of insulated ducting stretching about 8 to 10 feet to vented area), One 10 to 12 inch oscillating fan on high inside.

Also had to add an AC unit(8 or 9000btu) because we're getting into summer and temps in tent were hitting 90 degrees. And also I have a dehumidifier somewhere around 50 pints which sits outside the tent in the closed room and dries the air. A.C. was not powerful enough to be outside tent cooling the air inside so I had to hook up some duct fittings to directly blow air into the tent.

Sorry about the lengthy intro but that's my setup. Oh also I'm using soil. 21 plants in #2 pots, basically flowered as soon as they hit maturity. A mixture of 4 diff female strains accicently crossed with a male blueberry. Day 34 of flower.

So the problem is after I wake up each morning at 5am to shut the A.C. off when the lights go out, the humidity aparently rises quite high before lowering back down a bit. I have my DeHu on high speed continuous and RH is still spiking high at random numbers. Yesterday was in the lower 60s i believe and today I overslept by an hour shutting off the A.C. and it got up to around 77%, as of about 7 hours after lights off it was back down to 51%. So it seems to begin to spike right when lights go off. Idk if the variance in temp plays a big role in RH, maybe I can tweak my temps a bit to help. Temps vary 72-77 degrees and RH 38-lower 60s (usually), sometimes randomly hitting higher peaks, usually don't get below 38. My main buds are about quarter sized to over golf ball sized so I know that my time is ticking to get this under control. Please help with any input you may have

Or maybe with enough air flow is 60% okay?

NugHeuser said:

Or maybe with enough air flow is 60% okay?

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I run mine at 60% daytime 50% night time. No mold issues or PM

It's laborious reading but it has to do with Vapor Pressure. Also keep in mind the RH outside the house. Sometimes you can't get the humidity down. My plants run an average of 55%. Low of 44 to a high of 70% with a 45 pint dehumidifier running 24/7. If it rains then humidity is going to be high. Fog, dew point, and how much water evaporates out the pots.

Right after you water. The humidity will rise and then slowly fall over a few days. There's nothing that can be done about it. I experience 60% RH an hour after watering. Later in the day, 57. The next day 50. By that time the plants need more water.

The only way I see low RH in a 2x4 tent is if the outside of the house RH is really low. Currently it's 38% outside with 48 inside. Grow space has three ranges. I measure bottom, middle and top area of the plants.

Right at the pot it's 55%. Middle is 50%. Then the top area of the tent is 48%. The pot reads higher because water is evaporating. So it counts where you measure the RH.

Los Reefersaurus said:

I run mine at 60% daytime 50% night time. No mold issues or PM

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Sweet. If I had to i could probably hook up ducting from the DeHu straight to the tent but then I would have to figure out exactly when to turn it off and on to keep within ranges. But then It would raise my temps so I would have to keep the A.C. on more too which would probably change factors. Id just hate for my buds to mold, Idk how much it would take but a few plants are more than golf ball sized and rock solid

SouthCross said:

It's laborious reading but it has to do with Vapor Pressure. Also keep in mind the RH outside the house. Sometimes you can't get the humidity down. My plants run an average of 55%. Low of 44 to a high of 70% with a 45 pint dehumidifier running 24/7. If it rains then humidity is going to be high. Fog, dew point, and how much water evaporates out the pots.

Right after you water. The humidity will rise and then slowly fall over a few days. There's nothing that can be done about it. I experience 60% RH an hour after watering. Later in the day, 57. The next day 50. By that time the plants need more water.

The only way I see low RH in a 2x4 tent is if the outside of the house RH is really low. Currently it's 38% outside with 48 inside. Grow space has three ranges. I measure bottom, middle and top area of the plants.

Right at the pot it's 55%. Middle is 50%. Then the top area of the tent is 48%. The pot reads higher because water is evaporating. So it counts where you measure the RH.

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I see, that makes sense. The longest it stays at a high RH is just a few hours I'm thinking. I measure at the top of canopy. My plants are pretty small though. Mostly all India dominant measuring between 8" and 18" or so plus a lone sativa dominant that is barely growing any leaves and all nug, probably around 3 feet long, all trellissed, but is looking about week 3 rather than week 5. I've been pretty sloppy with watering, with the trellis in place the can tends to get caught here and there and spills water on the mat. I'll be careful and maybe that will help a bit

NugHeuser said:

Sweet. If I had to i could probably hook up ducting from the DeHu straight to the tent but then I would have to figure out exactly when to turn it off and on to keep within ranges. But then It would raise my temps so I would have to keep the A.C. on more too which would probably change factors. Id just hate for my buds to mold, Idk how much it would take but a few plants are more than golf ball sized and rock solid

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It's like 40 bucks, but you can get a humidistat on Amazon you can program high and low limits to control the dehumidifier. https://www.amazon.com/gp/aw/d/B005DK2T2Y/ref=sxts_1?ie=UTF8&qid=1499301064&sr=1&pi=AC_SX236_SY340_FMwebp_QL65