Dark Underside and Yellow/Brown Spots

[Cyberbong]

Hey fellow growes

Im new to this amazinf community and this is my first ever grow, but I'm having a bit of a problem with one of the plants. I checked the awesome Pictorial and other threads on the forums but had no luck in identifying my problem. Im hoping you guys can help me.

Heres my info:
-Indoor soil grow
-Soil: Substral Terra Magma (18 L):
-pH(CaCl2) 5,5 -6,5;
-KCL < 3g/l
-200-600 mg/l N
-200-500 mg/l P₂O₅
-500-1000 mg/l K₂O
-I added 50 g of Bat Guano
-4 plants - Day 9 from germination
-Strain: La Reina de Africa (indica/sativa hybrid (60/40%))
-250 W HPS (~45 cm above the top of plants; was 38 cm before today)
-Good Ventilation with an inner fan for circulation
-Temperature is 25 - 28 °C
-Humidity ~ 45 - 55 %
-I have no pH reading
-Im using tap water with no nutes

Im guessing it has to be an infection of sorts, since One of my plants looks like a beauty (I could be wrong) but the other one is lagging in growth and small spots, yellow at first started to apear (3 days ago), now some are growing in size and turning brown, Ive also noticed the underside of the leaves is dark (its not on the other plants)..

The following pictures show first my growbox then a healthy plant that germinated 12 hours before the sick plant (shown in the rest of pictures)

My growbox (in an old closet):

The normal plant:

Problematic Plant:

If you need any more info or pictures please ask me, I am anxiously awaiting any reply that could help

 

[David Bowman]

to

I wouldn't worry too much about the purple underside to the leaves at this point, keep an eye on them to see how they progress. There is no pattern to the burns marks, so if there are no pests of any kind, then it might be due to some water/nutrients spilled onto the leaves which then burned. I think it was a good move to raise the lights and you can raise them even higher as young plants can be quite vulnerable to close proximity HIDs. If the brown spots continue to increase in size or number, then I would check your soil for pH issues.

 

[Cyberbong]

Hey ColoradoHigh, thanks a bunch for your answer!

In the end those were the only leaves affected, they didn't even grow any more so I cut them of with a razor blade, was going to prune anyway.. so the plant I think is a beauty now, here's a picture

 

[David Bowman]

Looking very nice indeed! I take it that those purple patches have dissappeared?

 

[Cyberbong]

Sorry for such a late reply! They did thankfully =] Third week of flowering just went by, and I think they are doing good, only the oldest fan leaves are yellowing even after a lot of guano tea.. Not sure why, but its not hindering the growth at least.. (I think)

 

[David Bowman]

It's totally natural for mature leaves to start yellowing during flowering, starting at the bottom and working their way up, as the plant uses up its stores of N.

 

[Cyberbong]

I have read that about them naturally yellowing in flowering, but this started way sooner, about 3 weeks into veg.. here's a picture when it started happening:


Also I just posted this if you want to have a look how they look now =] Feedback needed - 4th week flowering

 

[David Bowman]

Stretch is done by 3rd week and the plant doesn't need as much N as during vegging but if you are still concerned you can feed them a little N but not too much or you could easily have additional problems.

 

[Cyberbong]

I fed them some more Guano, but I think its shit.. Couldn't get anything else here.. hope all goes well, thanks for your time Colorado!

 

[David Bowman]

No problem Cyberbong, you're welcome!