A sudden, unknown problem: help!

I just went to check out my babies, as I noticed that two plants are getting their top leaves yellow/orangy, they feel dry, and at the top.

Please check out the attached pics, any advice is appreciated.

could be a number of things coursing this but since i see mainly fan leaves turning yellow i would say it is coursed by the flowering, that the plant has not the power to support both, which can be coursed by not fair enough developed roots of in-mature plants i guess.

if you want to make sure that this is not something else you have to give a little more information such as:
soil/substrate you grow with
pH of soil if you grow with soil
fertilizers you use
if you pH that too and all pH of liquids you use
how often you water/ how do you water/how-much
temperature in the grow day/night
humidity
which lights you use ventilation of the room maybe

those things will help to narrow it down a bit more if something goes of the normal values or is just odd.

need more details...

I grow my plants in soil mixed with some dried clay balls. The bottom of the pots have a 5 cm layer of dried clay balls.
I'll test the pH tomorrow.
I water my plants every 2-3 days, or as soon as I see the plants drooping. I use regular tap water that has been left in a container for 2-3 days.
I use Biocanna fertilisers, during the vegetative stage I used Bio-Vega, mixing 30 ml every 10 litres of water. Now during flowering I use Bio-Flores, mixing between 30-40 ml every 10 litres of water.
The temperature is between 25-30 °C during the day, and slightly lower at night.
I have an oscillating fan going automatically on and off twice every hour for 10-20 mins all 24 hours long.
I use a 400 HPS lamp. 12 hours in flowering, 17-19 hours during vegetative.
I don't know the humidity.

from lookin at the pics id say u either have a potassium deficiency or a slight phosphorus deficiency, just use either chemical or organic nutes that have them. needs to have a n-p-k ratio over 5-5-5.

How far is your light from the top of the plants?They may be getting burned if they are to close.
Try keeping your fan on all they time during the light hours to minimize any heat build up.
Good idea to check your ph also, as tap water is often to high and can cause a nutrient lockup.
Last make sure your humidity isnt to low. Good Luck!

lights r fine and so is tap water (most of the time).

city tab water is not fine, it has to stand for several days so the chlorine can evaporate from it, city water is extensively chlorinated most of the time. in addition can be tab water far into the alkaline range as in my case it goes up to 8.5 sometimes usually around 7.8-8.0pH. so tab water has to be monitored for sure, guess why you are not supposed to put fish in fresh tab water but have to let it sit for at least a week.

MariJoe said:

I grow my plants in soil mixed with some dried clay balls. The bottom of the pots have a 5 cm layer of dried clay balls.
I'll test the pH tomorrow.
I water my plants every 2-3 days, or as soon as I see the plants drooping. I use regular tap water that has been left in a container for 2-3 days.
I use Biocanna fertilisers, during the vegetative stage I used Bio-Vega, mixing 30 ml every 10 litres of water. Now during flowering I use Bio-Flores, mixing between 30-40 ml every 10 litres of water.
The temperature is between 25-30 °C during the day, and slightly lower at night.
I have an oscillating fan going automatically on and off twice every hour for 10-20 mins all 24 hours long.
I use a 400 HPS lamp. 12 hours in flowering, 17-19 hours during vegetative.
I don't know the humidity.

Click to expand...

well your problem is not humidity, leave serrations turn brown and up then normally.
it could be that the water roods the roots away on your plant. if this is expanded clay it should normally let the water drain out but maybe for some hyte reason it isn't working that well so make a test set up, really pack and compress the soil in this and see if the water runs thru smooth or not. your pots also need drain holes in the button which are sufficient.

i think your fertiliser mix is quiet strong as i just checked the biocanna grow plan since i grow with hesi, do you monitor the pH of this at least in any way by using paper strips or anything??? if this isn't just from flowering you are in a starting pH lock up probably!

i think its nute burn or light but im only a beginner ?

Do you have something that sucks fresh air in and stale air out? You need to ph test all liquids before adding to your plants. You need to know the temp at the heigth of your tallest plant. Otherwise you don't know if it's getting too hot or not. You also need to know the humidty. If it get too high and you don't have fresh air brought in and stale air out there could be fungus problems. And that is BAD. Those spores go everywhere.

that is right mogie, but lookin on those pics and those yellow fan leaves i would say he got some problem that starts at the roots here. eighter nutes in lock up since he seems not to monitor the pH or root rot from dumping too much water on that pots. he states that he only waters every 2-3 days but not how much and if excess water drains out when he waters. you get that idea mogie?

I would like to hear back and have some of our questions answered. We can't make any type or diagnosis without more details. Hate when you try to help someone and they ignore your questions. Can't read your mind. Sorry physic powers are on the blink today.

First of all I would like to thank any one who is helping so far.

I don't think it is a matter of air circulation nor of having the lamp too close. The tallest plants are even closer to the lamp than the two plants with the problem, and are doing fine. Plus my hand doesn't get too hot when leaving it at plant height. I also don't want my plants to grow anymore vertically.
My ventilator is a moving one and quite strong. Heat buildup is inexistent.
The water drains perfectly out of the pots when I water them, and so it shouldn't be a problem of water.
I think roosterfish and green_nobody have hit the nail on its head: probably nute lockup!
As for the fertilisers, I am following the lower bounds indicated on Biocanna's website (i.e. if it says to use 30-40 ml of Bio Flores for weeks 4-last 2 weeks, I use 30 ml or slightly less).

Since I have to go water my plants now, I will use plain water with no fertilisers, and try adding extra potassium to the sick plants (thank you leafwrapper).
Haha I should probably save some money to buy a proper pH meter.

As you can see from the pics, I have had to use some yellow sticky paper to fight a fly invasion. Hope it's not THEM causing the probs.

I really hope it ain't root rot. I use about 270 ml of water for every pot every 2-3 days.

Bugs and ph problems. That will do it.

mogie said:

Bugs and ph problems. That will do it.

Click to expand...

I guess you're right. But I still can't figure out why the other plants are doing well. I have always given them equal amounts of h2o and nutrients, and just 2 plants have this problem. Wouldn't the other plants show signs of bad pH as well?