Fungus or burn?

Phosphorus deficiency.

Looks like a potassium problem. Next watering get plenty of runoff and test it's PH. If your grow medium ph is off then the plant can't use all the available nutrion it needs. If PH levels are in range it could be down to needing more frequent feedings.

potassium deficiency. Few things burn around the margins like that... low potassium is highly likely now, is it locked out or is it low in concentration? make sure pH is proper and consider any antagonistic relationships with K (see mulder's chart). If none of that seems likely, boost your K portion of formula as best you can without changing too much of the other levels of nutrients. same strains, same nutes doens't matter. the plant's behaviour is what matters. it is different, therefor something different is needed. could be that the fan is blowing on it (something in environment) or it could be genetics. Regardless, it's clearly not acting the same as the other plants.

It is likely ph related and or you need more bloom in feed.

Are you getting run off with feedings? might be a buildup in the soil. Some of it looks like root issues in the 3rd pic. My guess if that you need to get some runoff when feeding to avoid a salt buildup that causes other issues and have better aeration in the medium. Good Luck!

I grow in Coco but looking at the photos the tips of the leaves suggests a slight overfeeding/burn but the leaves them selves look a bit like calcium is needed. Idk maybe too much of something locking out cal maybe? It's not mold /fungus it's nutrient related.