Help me narrow down what's wrong - please!

[siu 3d]

Hi, I've been reading the icmag forums for months, reading up on setting up my grow. Finally got it finished-

3 bagseed plants in 16L pots, LST
0.8mx0.5mx1.6m tent
400w hps in cool tube with mag ballast
300cfm inline cooling fan and soon to be carbon scrubber

have been vegging under the hps for about 4 weeks now, and just in the last day, yellowing has started appearing around the tips of new leaf growth. slight burning even seen, just check the photo.

Plants had their first feed of half strength nutes about 6 days ago, after having been flushed in the bathtub full of water method. They're in 16 liter pots, with 30% pumice, 70% potting soil ("Max Yeild")

The symptoms resemble the description for: heat stress, low ph and Cal/Mag deficiency

my question is, which do you think it is, and how should i fix it? Is it even any of the things I've suggested??

I'll visit the hydro store to pick up something to test pH tomorrow as i have a sneaking suspicion that may be the problem.

Sorry if this is considered a noob question or wrong forum, I just don't trust my judgement on this matter. I've never had any problems with nutrient levels or ph in the past, with the soil mix and nutrient brands i've stuck to. however, I've only grown bagseed so consistency is impossible...

 

[bombadil.360]

if you were to ask me, I'd say you do not have a problem at all, that lil yellowing is just what happens when the plants start to need a little bit more nitrogen.

feed again, lightly, and see how she responds.

good luck

peace

 

[siu 3d]

my first thought was nitrogen too, but this yellowing is only present on the upper growth of the plant, doesn't nitrogen deficiency generally show up in lower growth first?

 

[bombadil.360]

yeah, you are right, usually n deficiency starts to show in the lower leaves; and not on new growth, I missed that part of your original post, excuse me.

why do you think it could be heat-stress? how is the humidity levels in there? air-flow?
I've seen some fungus that start to yellow the leaves a bit and then it makes them brown.

I'd still feed her lightly to see how she responds

good luck

 

[siu 3d]

It's around 27-30 degrees in the tent, it's the hottest part of the year in nz. humidity is fairly dry at this time of year, at least compared to the other months. it's a fairly warm+ dry room the tent is in

 

[juggo]

tent? could it be offgasing?

 

[bombadil.360]

um... and what about the air-flow? 30 degrees indoors is pretty hot. can you lower those temps and keep them between 22 and 25 instead?

 

[siu 3d]

shit, i hope not, It is made of pvc, but is this temperature enough to cause release of gas?

 

[juggo]

check the offgasing posts on here,that looks very similar too the problems they were having. good luck!

peace,
juggo

 

[juggo]

heres a link
http://www.icmag.com/ic/showthread.php?t=103953&highlight=tent+problems

 

[siu 3d]

okay, I'm going to get a cmh bulb tomorrow I think. cut down the heat a bit. then line the inside of tent with reflective mylar, to hopefully lower the temperature of the tent's material. What's the name of the foam backed reflective foil sheet stuff seen in some grows on here? I want to get some but don't know what to ask for.

 

[bombadil.360]

but temperature can be high enough to stress a plant; it does not have to kill it if the heat does not cross a certain threshold though.

 

[Hydro-Soil]

I doubt a Metal Halide is going to make much difference because since it's a HID lamp it'll still kick off the same amount of ambient heat.

Everything else you said was right on the money.

He meant a CMH lamp. Ceramic Metal Halide. They put off significantly less infra-red.... so your room doesn't heat up like it's a solar oven.

Stay Safe!