So I re read the entire thread & sorry I read this wrong I thought you were told it’s fungi
Now I understand it’s really common for new growers to think the worst & follow badly written manufacturers light distances.
Let’s start again
I don’t think you have fungus 100%
I don’t say 100% often however on this i am that sure.
You’ve more than one issue & that’s hard for you to fully understand et all
Firstly I want to emphasise how what we call incorrect watering can affect a plant it.
Too much to often & you’ll stunt the plant on the other hand if you let it dry out to much it’s littery drinking raw nutes & when you feed it when it’s to dry it makes the condition worse.
Secondly light is a major factor in a plant’s health to little & you’ll get slow growth , a stretchy plant with airy buds to close & your gonna bleach the leaves & stress out the plant.
Both these combined will have a diverse effect
Ok so your using very strong nutes.
Are they a synthetic mix in a bottle have you a link are you following a chart
Cannabis GROWERS SCIENCE group on FB
How often are you feeding
If you Listen to these folk you can get your plant back to good health however firstly you need to dim your light to at least 75% led lights are to intense for cannabis & raise them to 24”-38” away