All top leaves going yellow ???

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Chrisjames47

Active Member
Hello people I am just looking for some inputs, I am 7 weeks into flower and all the top leaves on my plants are turning yellow, I read it could be light burn but the closest plant is 18" away. I am using a 600w hps in a 4x4x7 tent with a 4" extraction and now I have a 4"intake fan what I set up yesterday to help with heat problems. I have one big oscilating fan blowing against the walls of the tent because it seems too powerful facing the plants and two 7" fans on the floor. The temperature has been between 25c-32c for the past week and humidity is usually between 55%-75% I know its high but I am hoping my new intake fan might help.
I am currently feeding once a day with canna a&b 1ml per litre untill around 40% runoff. I kepp my ph between 5.5 and 6.5 using drops now my meter is broke. The plant in the pics is the most yellowing one so I just took pics of that but there's 8 more in there and they are all like this.
Any inputs would be appreciated.
 

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Chrisjames47

Active Member
Thanks for the reply, right now the light is hooked on the top bar so I have ran out of height space. Do you think if I turned the ballast down to 400w it would be ok or hurt my yield?
Thanks again
 
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Chrisjames47

Active Member
Thanks mate, so if I just finish the grow for say 2 more weeks with feed and then flush would that be OK or will the buds be fried by then?
Cheers
 
hotrodharley

hotrodharley

Well-Known Member
Chrisjames47 said:
Thanks for the reply, do you mean that 20" is far enough away from the plants?
Thanks
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Depends on the temperature. A cheap IR thermometer is very useful in life. Use it to check leaf temperature. If it’s around 80 or less you’re good. I’ve run 1000 watts in a double wall insulated air cooled reflector and had plants 8” away. Lowe’s or Home Depot. Use to find thermal weak points around your house.
 
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Chrisjames47

Active Member
hotrodharley said:
Depends on the temperature. A cheap IR thermometer is very useful in life. Use it to check leaf temperature. If it’s around 80 or less you’re good. I’ve run 1000 watts in a double wall insulated air cooled reflector and had plants 8” away. Lowe’s or Home Depot. Use to find thermal weak points around your house.
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Ok I will look up the IR thermometer, thankyou for the advice.
 
wakenbake91

wakenbake91

Well-Known Member
Chrisjames47 said:
It's an open wing one.
Thanks
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I think the issue is heat tbh, try raising the light up some more and try to get a sealed air cooled reflector if you can. I know sometimes its not always possible bc money and what not but it will make a massive difference. And with that 600w I'd say you need a minimum 6" inline fan or something moving 400-500 cfm to move the hot air out. I used to use an open wing style at 400w and had all kinds of issues from the heat. I now have a 600w sealed insulated air cooled ( where the fan attaches to the hood) and I've had the plants less that 6-8" from the light and not had a single problem.
 
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Chrisjames47

Active Member
wakenbake91 said:
I think the issue is heat tbh, try raising the light up some more and try to get a sealed air cooled reflector if you can. I know sometimes its not always possible bc money and what not but it will make a massive difference. And with that 600w I'd say you need a minimum 6" inline fan or something moving 400-500 cfm to move the hot air out. I used to use an open wing style at 400w and had all kinds of issues from the heat. I now have a 600w sealed insulated air cooled ( where the fan attaches to the hood) and I've had the plants less that 6-8" from the light and not had a single problem.
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Ok thanks mate, I will look up some
wakenbake91 said:
I think the issue is heat tbh, try raising the light up some more and try to get a sealed air cooled reflector if you can. I know sometimes its not always possible bc money and what not but it will make a massive difference. And with that 600w I'd say you need a minimum 6" inline fan or something moving 400-500 cfm to move the hot air out. I used to use an open wing style at 400w and had all kinds of issues from the heat. I now have a 600w sealed insulated air cooled ( where the fan attaches to the hood) and I've had the plants less that 6-8" from the light and not had a single problem.
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Ok thanks mate, I will look up air cooled reflectors and I am planning to get a 6" extraction for my next grow.
 
Flowki

Flowki

Well-Known Member
Almost 90f temps, that's really high, where are your thermometers placed?. Also, 18" from a 600w open wing is a good distance as far as I've ever seen, so seems something is a miss?.

Oh sorry I see, it sounds like you need bigger in-out takes.
 
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Chrisjames47

Active Member
Flowki said:
Almost 90f temps, that's really high, where are your thermometers placed?. Also, 18" from a 600w open wing is a good distance as far as I've ever seen, so seems something is a miss?.

Oh sorry I see, it sounds like you need bigger in-out takes.
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Thanks for the input, yes I will be upgrading to a 6" extraction fan for my next grow. Cheers
 
Southernontariogrower

Southernontariogrower

Well-Known Member
My first though was ph is off the phos def but think ph is running low and locking out higher ph nutes. I used to fight temps with 1k hps but always had about a foot clearance. Even over 110 my plants did not do that. How long did you use broken meter and what did it read? Would help diagnosis alot.
 
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Chrisjames47

Active Member
Chrisjames47 said:
Ok thanks mate, I will look up some

Ok thanks mate, I will look up air cooled reflectors and I am planning to get a 6" extraction for my next grow.
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Southernontariogrower said:
My first though was ph is off the phos def but think ph is running low and locking out higher ph nutes. I used to fight temps with 1k hps but always had about a foot clearance. Even over 110 my plants did not do that. How long did you use broken meter and what did it read? Would help diagnosis alot.
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Thanks for the reply, I had the blue lab ph meter and it had some water damage so the digits on the screen went wierd but I would dry it out with a hairdryer before every use and it seemed to work but it ended up
Flowki said:
Yeah don't put that off, also sorry to assume your setup, but you only need an out-take for a single tent, and can rely on a passive intake.
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Cheers, do you think passive with just the 4" is enough for now?
 
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