First time grow...cant work out the issue!

[Site]

Apologies for a first post being one asking for help...i try to keep fairly anonymous on the internet but im a bit panicky at the moment as im on holiday for 3 days and a friend is looking after them for me...

Problem: This plant is the only one that seems to show the problem out of the 4 autoflowers that are in the tent. It is showing yellowing tips but leafs are drooping.
Medium: Biobizz Allmix in 16L Rhizo Pots
Feed: Plant Magic Old Timers Bloom 1ml per litre (half strength), water is tested to a PH of 6.7. I havent tested the run off though. They have only been fed twice in the last week. They are only watered/fed when they are pretty dry. I have been paranoid about over watering but they have taken around 1L each over 2 days.
Strain: Sweet Seeds Red Poison Auto - they are 5 weeks and a few days old since popping the surface of the soil.
Climate: Had constant 28°C On temp / 23°C Off temp (Rose to 31°C on today though)...humidity is around 55-60% but has risen to 70% a few days ago due to the weather we have had. Just bought a dehumidifier though.
0.8 x 0.8m tent, 400W HPS dual spectrum bulb, 5" fan exhausting to outside. I have 4 plants total in the tent and only this one is showing these issues. It is the tallest of the plants by around 3/4 inches though...light schedule is 18/6...

Additional info:

Ive had a look around the internet and read up and it to me it almost seems like heat stress but people say the leafs curl up rather than down, but I did read that they curl down when there is a potassium deficiency. Im paranoid about over feeding the plant, and also because the tips went yellow. They have all been fed the same (i only started a feed as the lower leafs started to show a bit of yellowing so I assumed they needed a feed, i could be completely wrong though! Im only a bit worried as its the only one showing any real big issues compared to the rest. Any help will be greatly appreciated! I have included photos of the plant in question and some overall shots of the rest to show their progress.

 

[Waira]

hey bud, I need pic of the affected plant in normal light,.. HPS is lousy for diagnostics, and color is often key to this,... that said, the tip frying and curl are overfertilization symptoms,..

 

[Site]

Thanks for the reply! my friend got some photos of it outside the tent earlier today. I think it looks a bit better out of the tent now ive seen it. We gave it a litre of plain water today with no extras, the yellow tips started just before we fed it oddly enough, maybe the allmix soil was a bit hot? I have kind of assumed it to be heat stress but not 100% at the moment...anyway heres some photos of it out the tent...

 

[Grim Reefer]

Hi @Site ,

Thanks for giving out so much detail when asking for help, it really helps.

So first of all we can see that the plant has been over fertalised. We can tell this by the very dark fan leaves and the fact that they are clawing downwards. This more than likely happened if you were using grow nutes or because the soil was a little too hot for your plant. I know you said this plant is the only one with problems out of all 4 but is there any chance that it had a slightly hotter mix than the rest?

The other thing i can see happening is lower older leaves dying off due to lack of light. Im sure it might be a little crowded in your grow tent or area and so some plants are more than likely shading the lower ares of other plants. A good way to solve this problem is getting some led side lighting, but to be honest its really not a big issue and its more than likely not needed.

I would think because this plant seems to be growing a bit bigger than the other 3 she will need to have used more energy and nutrients in doing so. This is why we are seeing yellowing of the mid- upper section of the fan leaves as she using more Phosphorous and Potassium. So because your plant is 5 weeks old, that means she has started her transition into flower and you can probably already notice some per-flowers or early development of budding beginning.

I would suggest that you slightly increase you Bloom feed by 0.25ml - 0.5ml per litre of solution for a week and see how well the plant responds to it. Let me know how you get on, please report back.

Now a quick question regarding the plants heat stressed leaves, how close are you hanging your 400w HPS from the plants canopy?

 

[Site]

Hope you dont mind i typed my responses in red below

Hi @Site ,

Thanks for giving out so much detail when asking for help, it really helps.

- Im on a few car forums and i get annoyed when someone just says 'i have a problem' with no information...it doesnt help you one bit when trying to give them a good diagnoses to their problem or why the car wont start etc! Thanks for your response though...just typed up the other bits in red to break it up

So first of all we can see that the plant has been over fertalised. We can tell this by the very dark fan leaves and the fact that they are clawing downwards. This more than likely happened if you were using grow nutes or because the soil was a little too hot for your plant. I know you said this plant is the only one with problems out of all 4 but is there any chance that it had a slightly hotter mix than the rest?

- Yea i havent fed any grow nutrients so far, just given the 1ml per litre of Old Timers Bloom over the past week as it has really started to flower. The soil was made up of 2 different 50L bags of biobizz all mix so maybe one was slightly hotter than the others but no idea to be honest.

The other thing i can see happening is lower older leaves dying off due to lack of light. Im sure it might be a little crowded in your grow tent or area and so some plants are more than likely shading the lower ares of other plants. A good way to solve this problem is getting some led side lighting, but to be honest its really not a big issue and its more than likely not needed.

- I wasnt to sure if the lower leaves were due to it needing a feed or another issue so thats helped me! I had read that when the lower leaves show signs of yellowing it means they need a feed, but im assuming your supposed to look more at the middle/top as a good indication? I have been tempted by getting a Mars 2 900 or a reflector 192 for the tent. I thought it may help with heat but im still a bit unsure to take the plunge...its my first time growing and i thought that the LED might be another thing on top of learning to learn almost!

I would think because this plant seems to be growing a bit bigger than the other 3 she will need to have used more energy and nutrients in doing so. This is why we are seeing yellowing of the mid- upper section of the fan leaves as she using more Phosphorous and Potassium. So because your plant is 5 weeks old, that means she has started her transition into flower and you can probably already notice some per-flowers or early development of budding beginning.

I would suggest that you slightly increase you Bloom feed by 0.25ml - 0.5ml per litre of solution for a week and see how well the plant responds to it. Let me know how you get on, please report back.

- I will talk to my friend and get him to up it to 1.5ml per litre and give her a feed and see how it goes.

Now a quick question regarding the plants heat stressed leaves, how close are you hanging your 400w HPS from the plants canopy?

The light is probably 15-20" away at a guess...its a 1.8m tall tent with a rhino pro filter and the light sitting around 3/4" below that on a euro reflector. I put it as high as i could get it really. Canopy temps are around 33 but have risen to around 35°C before. Is that an issue? My hand never feels warm let alone too hot when its above the plants with the light on.

 

[Grim Reefer]

No problem Site, glad i could help you dude.

In general to diagnose a plant, the grower must see the entire plant to judge the outcome and to fix the problem. So most problems have certain parts on the plant where they will show up but that is not always the case.

If im honest LED has a slight learning curve as each brand can vary drastically to the next but with HPS its pretty much a universal learning tool. If you have a 400w hps then the hanging distance from the plant canopy will be the same no matter what brand your have purchased.

Talking about HPS, a 400w should be kept above at least 18 inches above the plant canopy. Anything over 30c is way way too hot for your plants and this is exactly why they are showing signs of heat stress. Autoflowers optimum growing and flowering temperatures are 25-26c. Anything over 28c and the plants really start to stress and slow down. Have you invested in cool tubes for you HPS? If not this will sort out your problem with the excessive heat.

 

[Site]

Yea it was a harder one to judge as it seemed to be doing different things to the basic deficiencies I had read up on. It was much better to see out of the tent in proper light though...back off holiday now and it looks as if shes picked up a bit...i put my 250W hps bulb in and the temps are a bit more controllable.

I had no cool tube but tent is ducted directly to outside and the temps hadnt been an issue until we had some really really hot days...will try and keep the temps down considerably next time around...will grab some fresh photos tonight as well