Indoor Yellowing leaves with brown burning spots

[Highsnackz]

Can anyone explain for the reason of this discolouration and burn looking marks on the fan leaves? Is this due to too much light intensity or a deficiency i.e. calcium or mag deficiency? Any help would be much appreciated

Thanks!
View attachment IMG_20201008_191224.jpg

 

[namvet25]

Age of plant? Nute type and use?Calmag use? Type of soil and are you ph,ng?

 

[Highsnackz]

31 days old, biobizz root juice 4ml/litre on day 21 and 7g of biosy in 10l and 10nl biobizz grow between 3 plants the following water. Watered with water 2 days ago but issues have worsened. Growing medium being used is biobizz all mix. No calmag use. Was unable to pH the water so unsure about about the pH level but I have hard water in my area. See others having similar issues to me and they have said that it was due to the pH dropping below 5? Any thoughts?

 

[Highsnackz]

Oh BTW, day 26 had my telos 285w Pro 10 lights hung at 67cm although 80cm is recommended during veg. Think this has anything to do with the issues I'm facing? Thanks alot!!