Looking for general advice

Have only grown once before under a cheap 600W amazon light only draws 75W from the wall so super weak! Ended up successfully growing 3 photo plants and got around ~16g dry total, this took almost 3-4months but electric was only £15 on this cheap light so obviously terrible yield but only invested £80 into a diy grow box and this light so still cheaper than buying it and also alot more fun!

Skip forward some and I'm going again started 3 autos under that same cheap light about 3 weeks ago and the biggest plant is 61mm tall so doing really poorly not expecting much from them but it made me purchase a 400W HPS bulb (euro master reflector - not air cooled or anything just an open reflector) a 100*100*200cm grow tent and a 100mm fan (280m3/hr) with 102mm alu ducting - currently have both fans on 24/7

So here's where I'm looking for some advice the plants seem to love this new light but the tent is getting super hot saw a high of 34c last night with an average of about 35% humidity. I have the light right at the top of the tent and the plants are on the floor next to a 2-3 litre ish bowl of water and a basic oscillating fan, I have raised the plants and the fan about a foot of the ground this morning to help with air circulation. I'm venting straight out the window but the temps just keep climbing it was a hot day yesterday at around 26-30c so not expecting it to be super cool given the passive intact but was hoping it'd be a little cooler, I have a spray bottle that i've been spraying into the tent pretty often to get the humidity up and that lowers the temperature for a while but it shoots right back up once all that humid air is taken out the tent. I also lowered the light cycle to 13hours during the night to try and help temps but even at night the temps are still above above 30 as above

Is there anything else I can do to try to keep the temps a little lower I read all about stomata and all that and was worried the plants wouldn't grow but they have put on a decent amount of size since yesterday even in the hot temperature and seem to be doing pretty well this morning

Any help is massively appreciated!

Dont put thermometer in the light, seems like it if getting high temps at night and low humidity. Light shouldnt change humidity anyway so be the same for both lights not really a concern.

2Hearts said:

Dont put thermometer in the light, seems like it if getting high temps at night and low humidity. Light shouldnt change humidity anyway so be the same for both lights not really a concern.

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Yeah I've had the thermometer resting on the pots

Now I have the pots raised shall I put it in the shade under them?

The air temperature is dictated by your room temps not tent with good extraction.

If any light hits the thermometer it will warm it above air temps, at this point your reading light radiation not just air.

It needs shading and moving away from the light, anyone who puts a thermometer under the light of a hps will think its hot, just like if you put a thrrmometer outside in the sun.

You will work it out just keep the room the tent is in in check and good extraction will keep your tent in check, you dont even need a thermometer in the tent this way.

notagrower said:

Yeah I've had the thermometer resting on the pots

Now I have the pots raised shall I put it in the shade under them?

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2Hearts said:

The air temperature is dictated by your room temps not tent with good extraction.

If any light hits the thermometer it will warm it above air temps, at this point your reading light radiation not just air.

It needs shading and moving away from the light, anyone who puts a thermometer under the light of a hps will think its hot, just like if you put a thrrmometer outside in the sun.

You will work it out just keep the room the tent is in in check and good extraction will keep your tent in check, you dont even need a thermometer in the tent this way.

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Thanks man! I've lowered the lights and I've hung the thermometer above the light (now on) and i'm going to check back in 30 minutes and see how it's going

I've got 2 pretty big windows open in this small 3*3m room with the door open so airflow is pretty good through the room, the room temp should be pretty similar to the tent temperature though right with correct tent ventilation? The fan is just top draw the hot air away from the tent and the room so you don't suck the hot air back into the tent right?

I feel your pain buddy, hps in the summertime can be a pain in the a$$, forced intake and exhausting to outside helps alot, also a big oscillating fan in the room your tent is in will help, next step after that would be an air cooled shade, I had to make some adjustments yesterday due to the sudden change in ambient temp, 26c outside, tent was reaching 28c but I've managed to get it under control again

notagrower said:

Thanks man! I've lowered the lights and I've hung the thermometer above the light (now on) and i'm going to check back in 30 minutes and see how it's going

I've got 2 pretty big windows open in this small 3*3m room with the door open so airflow is pretty good through the room, the room temp should be pretty similar to the tent temperature though right with correct tent ventilation? The fan is just top draw the hot air away from the tent and the room so you don't suck the hot air back into the tent right?

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You should have the vent fan ducting directly outside and not back into the room the tent is in otherwise you’ll warm the room up and eventually lose the cooling effect ventilation has on the tent.

RANGERTHEDOG said:

You should have the vent fan ducting directly outside and not back into the room the tent is in otherwise you’ll warm the room up and eventually lose the cooling effect ventilation has on the tent.

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Yeah the exhaust is venting out the window

Anonymousgardener420 said:

I feel your pain buddy, hps in the summertime can be a pain in the a$$, forced intake and exhausting to outside helps alot, also a big oscillating fan in the room your tent is in will help, next step after that would be an air cooled shade, I had to make some adjustments yesterday due to the sudden change in ambient temp, 26c outside, tent was reaching 28c but I've managed to get it under control againView attachment 4605510

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What's that bag hanging there for?

Anonymousgardener420 said:

I feel your pain buddy, hps in the summertime can be a pain in the a$$, forced intake and exhausting to outside helps alot, also a big oscillating fan in the room your tent is in will help, next step after that would be an air cooled shade, I had to make some adjustments yesterday due to the sudden change in ambient temp, 26c outside, tent was reaching 28c but I've managed to get it under control againView attachment 4605510

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Nice man! Yeah I bought this light without much in the way of research should've paid a bit extra for an air cooled hood but wasn't planning on getting a tent and everything else so kinda stuck with it now -.-

I have a single 12inch oscillating fan at plant level pointing up at the light slightly, the temp went from 28.5c to 32.5c in half an hour with the thermo hung about 20cm above the light, but obviously light bouncing around a lot so going to measure the temp of air in front of the passive intake and see what kinda temp air is being pulled in think i need another fan on the light or just suck it up and get a cool tube or an air cooled reflector think that'd make a big difference

Thanks all for the help!

The fan sucks out hot air and draws in cooler air from the room, you have windows and doors open so it should disperse not build.

Easy to tell what temp the air going in your tent is just put thermometer outside tent in the room.

There is prob no real perfect place for a thermometer in the tent, you will find it fluctuates a small amount in different places as well as wildly under the light. Rather than an answer i just want to draw you into the small amount of science needed to accurately measure air temps, them hps arent that hot but they are bright and that can piss a plant off if too close as light can overheat a keaf much more than air, air balances the cooling effect more.

Small things just do a lot of grows it will get simpler over time .

notagrower said:

Thanks man! I've lowered the lights and I've hung the thermometer above the light (now on) and i'm going to check back in 30 minutes and see how it's going

I've got 2 pretty big windows open in this small 3*3m room with the door open so airflow is pretty good through the room, the room temp should be pretty similar to the tent temperature though right with correct tent ventilation? The fan is just top draw the hot air away from the tent and the room so you don't suck the hot air back into the tent right?

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2Hearts said:

The fan sucks out hot air and draws in cooler air from the room, you have windows and doors open so it should disperse not build.

Easy to tell what temp the air going in your tent is just put thermometer outside tent in the room.

There is prob no real perfect place for a thermometer in the tent, you will find it fluctuates a small amount in different places as well as wildly under the light. Rather than an answer i just want to draw you into the small amount of science needed to accurately measure air temps, them hps arent that hot but they are bright and that can piss a plant off if too close as light can overheat a keaf much more than air, air balances the cooling effect more.

Small things just do a lot of grows it will get simpler over time .

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Yeah I'd agree, I think seeing 30+ just scared me a little, currently close to 30c outside the tent so can't expect lower temps inside the tent as long as the plants are growing I'm happy learnt a lot from this though so thanks again!

Well the idea that the tent will be the same temp as the room when you've got a light on is nonsense.
It takes around 1000-1100cfm to keep a space 1degree C above ambient room temp with a 600w light.
Which is massively more air flow than your average 3 exchanges per minute.

The concept that lights don't heat air is flawed , just because light isn't very good at heating air directly due to its mass doesn't mean the air doesn't heat up.
It just heats all surfaces which in turn heats the air which heats the air next to that and so on, plus a bulb runs several hundred degrees C and heats the air its in contact with pretty well.

Sorry those specs are whack, the tent walls would be hot to touch at lower cfms like we run. You dont need that much air to remove 600w of heat and thats the cooling effect leaves experience too or a 600w would straight kill a plant.

coreywebster said:

Well the idea that the tent will be the same temp as the room when you've got a light on is nonsense.
It takes around 1000-1100cfm to keep a space 1degree C above ambient room temp with a 600w light.
Which is massively more air flow than your average 3 exchanges per minute.

The concept that lights don't heat air is flawed , just because light isn't very good at heating air directly due to its mass doesn't mean the air doesn't heat up.
It just heats all surfaces which in turn heats the air which heats the air next to that and so on, plus a bulb runs several hundred degrees C and heats the air its in contact with pretty well.

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PadawanWarrior said:

What's that bag hanging there for?

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Co2 bag

2Hearts said:

Sorry those specs are whack, the tent walls would be hot to touch at lower cfms like we run. You dont need that much air to remove 600w of heat and thats the cooling effect leaves experience too or a 600w would straight kill a plant.

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Its a scientific formula dude used in many industries . Anything that involves wattage and airflow or a space that need to be cooled due to the mechanics inside it.

The reason the tent walls are not hot is because a hot surface will always transfer heat to a cooler one.
In this case walls to air by conduction and then air to air by convection. Same with the bulb, conduction then convection.

Its basic thermal dynamics

Anonymousgardener420 said:

Co2 bag

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That's what I thought. Just curious.

You cant see your error its not my fault you think you need ultra airflow with hps, 1000cfm, holy cow thats a hurticane tent not a grow tent.

But the point was if you put a thermometer under anylight its not going to read the right air temps and why he thought a hps would be too hot.

coreywebster said:

Its a scientific formula dude used in many industries . Anything that involves wattage and airflow.

The reason the tent walls are not hot is because a hot surface will always transfer heat to a cooler one.
In this case walls to air by conduction and then air to air by convection. Same with the bulb, conduction then convection.

Its basic thermal dynamics

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2Hearts said:

You cant see your error its not my fault you think you need ultra airflow with hps, 1000cfm, holy cow thats a hurticane tent not a grow tent.

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I don't, I can afford to have plenty of rise from room temp in my house. But you said have the room at the temp you want the tent to be which means zero room for increase in temp, which was my point.

2Hearts said:

But the point was if you put a thermometer under anylight its not going to read the right air temps and why he thought a hps would be too hot.

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I fully agree with that and always have KG.

Have you tried running lights on during the night and lights off during hottest time of day?