Brown spots on some leaves

[TheClem]

Hey guys !

I started my first grow a month ago, and everything seems mostly fine for now.

Here's a pic of the babies, I think they seem pretty healthy... ? The 2 on the left are Runtz, and the 2 on the right are Crystal White.
The smaller one is a week younger, one of my seeds didn't sprout and I had to start an other one.

First question : should I be worried about those curly leaves on the smaller one ?

Second question : since a week or so, I noticed brown dry spots on some leaves (see pics below), 2 mostly, but it started on 3/4 others too.

Any ideas on what it could be caused by ? From my internet researches, it seems it could be related to a fungal infection ?

Some additionnal informations :
- I'm using BioBizz starter pack as fertilizers, and I'm following the calendar they give for quantities.
- They're under a LED full spectrum light, a MarsHydro TSW2000.
- Pots are 18L, and I'm watering with 1.5 to 3 liters of water / pot every 2-3 days.

Feel free to ask any futher informations required, and thanks for your help !! :)

 

[mancorn]

Doesn’t look like a fungus. What are you growing in? Do you test your pH?

 

[TheClem]

Doesn’t look like a fungus. What are you growing in? Do you test your pH?

I'm growing in Light Mix, don't remember the reference but it is close to the BioBizz Light Mix.
I test my PH systematically yes, and keep it between 6 and 6.5.
I use tap water, but let it rest 24h before using, to let chlorine and such evaporate.

 

[mancorn]

Not familiar with your medium, but don’t think it’s an actual soil and not used for a full grow. Hopefully someone experienced with Biobizz can help.

 

[GNick55]

all from overwatering- watering too frequently..