Been trying to read everything I can for what I need to do in future. My girls are about to go into the vegetative state. On reading last have a 400 MH bulb for this stage. Reading on its advised to use 600 MH for flowering.
My question is this: got a 39 X 39 X X 72 tent. Live in SW usa and have had tremendous problem with keeping temp down. My grow tent came with this HP. If I go to a HP 600 won’t my temp increase? If I don’t and use the 400 HP what will it do to the girls?
ok so with the temps the best thing you can do is buy a DECENT extraction kit… something that’s capable of pulling serious Cubic ft per minute, you want something like ipower 6inch inline fan… if heat is still a major issue try using a cooltube lighting… i am in UK and have MAJOR issues with heat was pushing 100f last summer so switched to a cool tube now i can hang around 78-83
running a 400w halide will be fine for the veg stage they will love that, but for flower with a 3.5 x 3.5 I’m not sure the 400w HPS would cut it… yes they will flower but i fear the yield might suffer significantly compared to running a 600w HPS… that being said could consider buying 2 300w LEDs which wont give off any heat and use the 400w HPS alongside 2 x 300w LEDs when you get into flower 
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So the 600 will put off alot more heat? I’ve already installed a 260 duct fan at bottom of tent & put window unit in room set @60°. Are the led expensive & aren’t there certain colors or hues?(as you can see I know nothing about led) Also do you mean cooling tube for reflector?
so the fan is sucking from BOTTOM of tent? if so that’s an issue…
yes a 600w HPS will add a fair bit extra
Not really now a mars 300w will cost you about $70 each and are dual for veg and bloom…
HID bulbs... Which one? - #34 by majicmarkers a similar conversation going on here I’m having with more experienced growers
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Thanks for pic!
No the duct fan is blowing cool air into tent from the room it’s in. Exhaust is mounted in top of tent w/2 sm fans blowing. So 3 fans with air in & one air out.
Also many thanks for info on led. Will checkout as I’ve got couple weeks before needed. Trying to get everything together
What CFM is your exhaust fan?? because that’s where you will get rid of excess heat
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That I don’t know. I bought a supposed to be ("all you need to grow tent ) and exhaust fan and carbon filter included. Will look when I get home
they tend to be cheaper fans something with a bit more guts is needed probably
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Thanks for All your help! Sure you’re right about exhaust. What about a 400+ for exhaust? Think I’d be ok with 600 HP with new exhaust?
yes 450cfm my exhaust fan is… and i use a 4 x 4 with 600w HPS can get to mid 80’s still but that’s when the sun is beating through my window
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Awesome, your information really helped! Going to check as soon as I get home & order one from Amazon. Great two day delivery and a 600 HP.
Many thanks!
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Happy to help when i can 
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Will I need to buy another ballast? Or will mine support a 600HP, or is that a stupid question?
if it was a complete grow kit all inclusive I’m going to guess that it would be a 400w ballast… it should say on one of the ends but I’m going to guess you would need a new ballast too 
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@Donaldj, I saw on another post you’re using 400Hp for girls. I’ve got a 39 X 39 X 72 tent in my bedroom. Will it be strong enough for 6 plants. I’ve been reading Roberts grow schedule & he calls for a 609Hp for grow & afraid it’ll be too much heat. Got the exhaust inside with two fans & a 269 duct fan pushing more cold air in at bottom. Also got a window unit (have central a/c) set @ 66°.
Please advise,have been told to get cooling tube , but also if I go to 600 would I need a new ballast?
A 400w HID MH/HPS if used correctly can work for around 4 plants in a 36x36 foot print but your plants have to be kept smaller and trained since the light will not penetrate a thick canopy. I use about the same foot print but I am using a Screen and in Veg they aren’t as demanding for light intensity during flower light needs to be kept closer.
Will it work yes for 6 plants no, Will temps be cooler and easier to control yes.
600w HID is still considered one of the most efficient HID lights based on Lumen and Lux per/watt
I have phased out all but 1 400w in my grow for 315w LEC’s I am not going LED anytime soon as I live in a climate that I spend 8 months or more heating so my lights provide the heat
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Thanks, unfortunately where I am it’s already 90° and by August will be topping around 105°. I’ll be in 100s till September. I’m already committed to using mh and hp but ordered the 600. Think a cool tube will help? The girls will be asleep during the day to help fight temps.
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Cool tubes work very well I have used them in 5x5x7’ tent with 1000w HID with decent results but make sure it get fresh air from cooler space and vents straight outside closed loop possitive pressure
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Thanks, I’ve ordered the 600 HP as well as a cooling tube. Think we’ve got all hot air vented outside and have an a/c set @ 60°. Also, in morning I open windows for fresh cool air
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