Probably overheating problem. Need advice, please.

[BengBong]

Hi everyone. I am new to this forum and this is my first grow.
I need some advice because my plants do not look healthy. In the beginning of September I planted 8 Light oh Jah plants from seeds. They were under constant light (24/0) for 3 weeks and for the last three days they're geting 18/6. First 14 days they were doing pretty good but than I had some problems with ventilation and plants were in quite warm environment for a day and a half. They had enough water but the air was probably above 30 degrees C (86 F). In next couple of days majority of fan leaves turned yellow with brown spots and I cutted them off. All leaves on all plants are now light green and each day a few new leaves turn yellow with brown spots as you can see on the photo. Since the ventilation problem the growth is very slow.
Soil mixture: worm castings, compost, coco, perlite, rock dust. I did not use any additional fertilizers. PH is 6.5. The plants are low stress trained. The temperature in the grow room is usually between 25 and 27 degrees C (77 — 81 F). When the sun is shinning I take them outside so I am moving them quite often.
Can you give me any advice on how to restore my plant's health, please.
First photo was taken before the heat shock and the other two were taken yesterday.

 

[Antics]

How often do you water them?

The brown spots look like a calcium deficiency. The yellowing of leaves, if starting at the bottom of the plant, is likely a Nitrogen deficiency. On your plant it looks like it also might be a magnesium deficiency.

Don't cut the leaves off with spots. The leaf can still benefit the plant, and this will not make the problem go away, what will happen is the problem will just show up on another leaf.

It sounds like you have a pretty good soil mix, but the use of additional nutrients for Cannabis is necessary, it's a very hungry plant.
I recommend that you do not use fertilizers like miracle gro, or any time release fertilizers/nutrients.
I suggest using a nutrient system that is 2 or 3 parts, and requires you to measure and mix individual batches. I have had the best luck, as have most other growers with this type of nutrient system.

 

[BengBong]

Thanks for the advice. I will add some fertilizers.
I water them once per two or three days just enough that water come out from the bottom of the pot.

 

[Antics]

Make sure you allow the soil on the top to become completely dry, and after that, wait a few more days before watering.

Cannabis grows best with an ebb/flow style of watering. It receives plenty of water until there is some runoff from the bottom, then there is no water for days. This forces the roots to stretch and grow bigger inside the pot